Local doctors office bill went to collection. Not notified

I had a bill with a local doctor's office. They only claimed to have one person working in the office and when my husband and I called to request statements - it was always an issue of they'd print it out and mail it that day. Well - we never received the statements - time passed and we finally received one that said we were being sent to collections.

So now here we are trying to get in touch with a well known collection agency. The number we dialed never worked and would always cut off. Finally my husband went through several prompts and said we had 4 months to pay the total - which was only 180.00. We decided to break it up into 3 months and send payments. When they woman finally called - she said I would not like the letter I requested with the remaining balance. To sum it all up we could never get in touch with the agency and now it's showing up on my credit report.
-------------------------------
you made a mistake by paying without confirmation
its ok though
what to do now.

dispute the account as paid in full zero balance
get the results and mail your payment copies to the address provided from the dispute if the dispute is verified and they say you still owe money. if not its over.
then validate the debt with certified delivery mail
go all the way to state attorney general if needed.

you said you paid and it still shows up
so that is the assumption i am making here

really one should try to negotiate with the doctors office first. Read what I did on that page.
but in this case someone has taken your money and something has to be done with them