Old paid up retirement policy

This is a bit complex but I would appreciate your input.
My wife has an old paid up retirement policy which was deemed, 'paid up' back in November 1993. I sent an inquiry to the Pru asking if it was of any value. They eventually wrote back saying that this policy was paid out in 1996. We are very much confused because we have never had a payment from them. They sent back some scanned copies of documents of which 1 had a forged signature of my wife's, and another that had a genuine signature, on a document that we have never seen. We have been in touch with my wife's bank, but their records only go back 7 years. Is there any way of obtaining records of statements that go back 10+ years? Also, the Pru have said that they only hold records of cheque payments for 7 years. The amount in question is around £2000 and we are not wealthy, if this sort of money was signed for 10 years ago, we would have been waiting for the postman.
Any input at all will be welcome, thank you.