I'd find out if this lender is a member of the Mortgage Lenders Council (there is a website). If they are, write back and tell them that as this "debt" is now 8 years old and you have had no correspondence before, they are out of time (6 years is their agreed limitation period).(posted 7632 days ago)If they write back to you after that, you need to do as Mark says and put them to strict proof of the debt.
Good luck,
Tracey