Cathy,
Brat is right. You should dispute the item with credit bureau. Supply whatever document you have. Bureau will run an investigation and update your file accordingly.
Anyway, did you pay the amount to the hospital or you paid it to CA? it is their responsibility to update your report who received the payment I think. Since they are playing game with you, let the bureaus handle this issue.
You can dispute with credit bureaus through correspondence, over phone or online. Please visit this page to get some idea on how to dispute an item online-
http://www.debtconsolidationcare.com/video/disputecreditreportentry.html