Did you pay after bills stopped being sent, or did you pay a current bill that had a due date. If it had a due date and you paid before that date, I think you would have a valid complaint.
If you paid the bill after the date, they may have already changed it off and the reporting process is catching up with you. I am sure the bill has some comment about serious deliquency blah blah blah in fine print at the top of the bill in the special messages section.