NCO did the same thing with me. Sent me a settlement offer, I paid it, and they were still calling and leaving messages five months later. When I finally spoke with one of the reps, they didn't have any settlement offer listed. It was only because I'd made copies of everything and had to fax it to them when they finally closed the acct with zero balance. But still have them on my CR as 120+due paid. Documentation, documentation. I'm in current dispute over the 120+ late with them.
Ficos
3/7/08 TU-646 EQ-640 EX-650
3/17/09 TU-678 EQ 666
3/20/12 TU- 760 EQ 785
Util almost 0 and baddies all gone! now to gardening!