I was contacted by a debt collection agency by phone stating that I owed $686.00 from 1991. I returned the call to find out what this pertained to and the gave me the name a store credit card that I had at that time - during that period my ex- husband filed bankruptsy and all accounts ( personal and business) were turned over to the court. I have no records dating back that far... when I hung up the phone and realized they had said 1991 - I COULD NOT BELIEVE IT! Anyway, I sent a letter stating that it was past the statue of limitations in NC and not to contact me. I got home today and had a message stating they received my letter and I must contact them today. What should I do ?

Nothing, they can attempt to collect a debt after SOL, they just can't take you to court.

You told them not to contact you, so they already broke that rule, don't call them, and don't talk to them on the phone, make them do it in writing only.