Back in 1989, I bought a flat with my then-girlfriend. We got an interest-only mortgage with Abbey National, now part of Santander. 

To make sure we could repay the mortgage, we took out an endowment insurance policy with Friends Provident (now Aviva) - an investment vehicle which would pay out at the end of the 35-year term in 2024. 

The relationship ended shortly after, and my girlfriend moved out. I stayed in the flat until 1999 when I sold it and repaid the mortgage from the proceeds. 

I kept paying the endowment insurance premium until around 2009. I didn't keep in touch with my former girlfriend, but later found out she sadly died in 2015.

In early 2024, I got a letter from Aviva stating that the endowment policy I took all those years ago would mature in August 2024 and that there was money due to me. I think it is at least £24,000. 

However, it said that according to its records Santander still had an 'interest' in the policy - which shouldn't be the case as the mortgage was paid off 25-plus years ago.

To get the money, Aviva said I needed to ask Santander to confirm in writing that this was not the case. 

I requested this in April 2024 and still don't have the proof I need. Santander says it doesn't hold any information relating to my old mortgage account, because it was repaid more than six years ago. 

I've given it the original mortgage agreement but it still hasn't managed to sort it, despite my many efforts.

I'm now in poor health and could do with the money. Can you help?  A.B, Kent

Helen Crane, This is Money's consumer champion, replies: Endowment policies are seldom heard of these days, but were common in the heyday of interest-only mortgages in the 1980s and 1990s. 

They offered borrowers the opportunity to take advantage of the lower monthly mortgage payments that interest-only offered, but then use an investment plan to clear the balance at the end of the term.

When you took out your mortgage the rate was an eye-watering 13.5 per cent, so I can't blame you for wanting to keep costs down.  

Endowments essentially combined a long-term investment vehicle with life insurance. At the outset, customers agreed to pay in a set amount each month for a fixed number of years, usually to match the length of their mortgage term.

The money was then invested, and at the maturity date they would get a pay-out. How much depended on how the investments performed. 

Many policies also included a death benefit, which would pay out if one of the beneficiaries died during the term. 

But they were by no means risk-free. As a growing number of the policies reached maturity in the 2000s, many found they didn't get the returns they were promised and this sparked a major mis-selling scandal. 

Some were told at the outset that they would have enough to pay off the mortgage at the end of the term, and a sizeable lump sum on top. 

But stock market wobbles over the years, combined with the opaque nature of with-profits investing, led their investments to severely underperform.

Some were left with no option but to sell their home to pay back the bank. 

Having moved on from the home you took the endowment policy on more than 25 years ago and cleared the mortgage, this thankfully wasn't a worry for you. 

However, you told me you have some health problems, and this money would help you afford to retire from your job as a flooring fitter. 

Aviva - which acquired Friends Provident in 2015 - has sent you statements over the years, and the most recent one said the policy was worth around £24,000. 

It is just as well you don't have to repay the mortgage on that flat, as you bought it for £56,000 - though if you hadn't stopped the payments, that sum could have been higher. 

You say you did so because your financial circumstances changed and you could no longer afford it.  

While your ex was named on the policy and has died, you forfeited the death benefit because you stopped making payments before the maturity date - so this was not owed to her estate. 

Your former girlfriend didn't contribute to the endowment insurance payments, though she was named on the policy, so her estate would be unlikely to have a claim on the payout. 

Why was it difficult to get the money? 

In February 2024, you received a letter from Aviva stating that the endowment policy would mature in August. 

All you needed to go to get your money was to complete the simple admin task of getting Santander to state that it no longer had an interest in the policy, as the mortgage had been paid in full. 

But that process turned out to be far from simple. You asked Santander to provide this in April 2024, and it did - but it omitted the policy number, so Aviva couldn't use it as proof.  

It claimed it sent a replacement letter, but Aviva maintained that it never received sufficient proof. 

Then, in May, your first letter to Santander was posted back to you with a note that said that the mortgage account number appeared to be incorrect, and that 'if the mortgage account was repaid more than six years ago, we will no longer hold any information relating to this account'.

It is the policy of many financial institutions to destroy records more than six years old. This is because it is the length of the statute of limitations in most financial matters, meaning the documents could not be called upon as evidence in a legal case.  

I understand the need for data protection, and that maintaining vast servers filled with information incurs a cost to banks - but I would argue that six years is far too short for a mortgage term. 

Storing information has to be easier today than in the time when paper records were stored in miles upon miles of filing cabinets. 

Six years is not a terribly long time when it comes to our finances, and in my experience writing this column, I have come across many readers who have fallen foul of this rule and struggled to sort out their affairs. 

Luckily you had kept your records for longer, and were able to send Santander a copy of the original mortgage offer letter dated July 1989, including the account number. However, this was also returned to you, this time without explanation. 

You phoned Santander and were given an email address to contact, but didn't get a reply. 

In October, six months since you first wrote to Santander, you visited your local branch and the manager sent all correspondence about your mortgage to head office. 

But still, by November Aviva said it hadn't heard from Santander. 

You had by this point provided all relevant information to Aviva, including obtaining a copy of your former girlfriend's death certificate, but it told you it was unable to proceed further until a letter of no further interest in the policy was received.

That is when you contacted me, and I quickly asked Santander and Aviva what had taken so long. 

Santander said the information on your mortgage had been difficult to obtain, because of the time limit on retaining information. 

However, within two weeks of me getting in touch, it had managed to locate the files that it needed and send these on to Aviva. 

You have now received your payout, which totals £25,150.

Santander has also said it will pay you compensation, and you are in discussions over how much that will be. 

A spokesperson for Santander said: 'We are sorry for the length of time it has taken for us to investigate A.B's case. 

'We appreciate that it has taken longer than expected to provide details required to Aviva and confirm the claim has now been paid. As such, we would like to apologise to A.B and offer him compensation.'

A spokesperson for Aviva added: 'We were not able to make the payment to our customer without the relevant documentation from Santander giving us the authority to do this, as they were named as having an interest in the property.

'We received their confirmation last week and we made the payment immediately.

'We are sorry for the inconvenience that A.B has faced in ensuring both Santander and Aviva had the correct details to enable the payment to be made.'