I have had and am having the SAME EXACT PROBLEM!
NCO contacted me 3 years ago about a PECO bill. I paid them in full. Last June, I was contacted by a completely different collections agency (CBCS) in regards to the same balance! I contacted NCO and they acknowledged my payment in full. They said they would send me a letter of proof that I could provide to CBCS. While waiting for that letter, I contacted CBCS, letting them know the exact matter of the situation.
I am STILL waiting for that letter from NCO. In the meanwhile, I have just received a second letter from CBCS saying that I am still delinquent and when I called CBCS letting them know yet again the situation and how this no longer has to do with me, I am told that it is my fault and I will be reported to the credit agency.
This is messing with my blood pressure and I am a fit person of a mere 26 years of age. THERE HAS TO BE A MORE EFFECTIVE WAY TO STAND UP TO THESE AGENCIES!!!!!
What the hell do I do now?!