Dentist/insurances Mix Up Got Me Wrongfully Sent To Collections. Iowa

I had a procedure done at the dentist a couple years ago and paid my part. A couple months later I got another bill from the dentist saying I owed more money. I called them and was told that I should disregard that because that bill was supposed to go to my insurance company.

But I recently got a call from a debt collector saying that I was sent to collections for an unpaid dental bill. I called the dentist and their customer service said that insurance denied the claim due to a late filing by the dentist so it shouldn't have been sent to collections. Then I talked to someone in the office and they said insurance was supposed to give them a grace period because their systems were down. I'm waiting to hear back from the office manager of the dentist. What else do I need to do?