Merchants' Credit Guide Co. bogus letter for debt that was paid YEARS ago Chicago Illinois

Ok- so here's what I want to know. I got a letter from these jerks stating that I still owed a debt to "NCO Financial". I (not knowing) called to find out who the heck that is. They told me Pottery Barn.

Well I had a Pottery Barn card years ago (first apartment, too much debt) which *DID* go to collections, back then, and I paid it as a charge off (where they have you pay a certain percentage and the rest is written off). I also did the same thing back then with a Pier 1 card. I've since had Pier 1 try to come after me again saying I owed them the amount of the charge off still- which I disputed and won. NOW I get this crap from Merchants Credit saying I still owe Pottery Barn. Who by the way uses World Financial Bank, not NCO for their collections. This credit card is from 2002. I think they are trying to collect either on the charge off amount (which I'm having trouble proving...I've moved 3 times since then and have NO idea where those records are.) Do I have to prove to them that the debt was paid? Should I try contacting the bank who issued me the Pottery Barn card to find out if they show it as paid? I KNOW that I paid it. I just don't know where the proof is. Though if it IS past 7 years do I even have to show them proof or just tell them to shove it?

Before realizing I should send it certified mail I sent a letter (which I did keep a copy of) stating I was disputing the debt, that it had already been paid, and that I had informed a representative of that fact when I called. Now I'm wondering if I should send a second, formal, certified letter tomorrow telling them not to contact me, the debt has been paid, and to shove it.

Advice?

Stephanie
Idaho City, Idaho
U.S.A.