Keep calling??

I received a bill a little bit Shai that I lost. It was from a collection agency for like a $600 bill that I had never been informed of and never received a previous bill for. I called and they said my insurance finally kicked in and paid for it. So then a little bit Shai I received another bill. So today I called the hospital and they said I do not have a balance, but it might be from the radiology department and I would have to call the radiologist to find out. Well I have been calling and left messages and he won’t answer or return a call. I need to get this figured out before my tax returns get here this week so I know where and how much I need to pay. Should I keep calling him today or no?