I got a call a month ago about a bill I supposedly owed at a medical clinic that I used several months earlier. I told the collector that I had insurance and the insurance paid. The collector said they would mail me a copy of the bill showing the amount I still owed. Nothing has come and the calls stopped. Don't pay a bill just because some collector says you owe it. Get the information. It could be that a clerical error has been made. It could be that the collector is a scammer.
I went through the same thing a few years ago after a shoulder surgery. Separate bills came from the hospital, doctor and the imaging company that did the MRIs. With all of the bills insurance took a while to pay and the hospital sent me to collections. Insurance finally paid but the collections agent was not pleasant to deal with and it was a pain to remove from my credit report. I don't know any personally but after what I went through in that case, collections agents are scum.