The old debts became statute barred after 6 years. You should send a letter similar to the one linked below.

http://www.moneysupermarket.com/community/forums/post/statute-barred-160856.aspx

If you have the agreement in writing for the other debt, you could write to say that ther recent correspondence contradicts the agreement and, unless the situation is clarified in writing within 30 days, you will be stopping payments until such clarification is received.