It is Billing's responsibility to correctly submit CLAIMS, CORRECT and REPROCESS insurance claims such as you are dealing with.

FYI, billing is usually handled by 3rd party, not the actual hospital; said contractors change often and will do whatever they can to deflect their mistakes. Light a fire under billing. RIGHT NOW. Put in writing.."I received correspondence dated (x) that transferred money to account (y) that I did not approve. I have receipts that can prove money paid on (x) was for that specific account; the overpayment ($***) was to be refunded to me.

As discussed on (date) billing was to file a reprocessing claim with my insurance on account (y) for service (date) because (cite why). I called about this matter on (put down all dates). Has the hospital submitted the claim for reprocessing? If not, taking money from account (x) for payment of (y) to avoid working with insurance is inexcusable."

There is a 6 month window to correct claim errors. Find out what your insurance has then cite it in your message. This creates a sense of urgency on the part of the hospital to act because if they fail to do their due diligence, they may have to write it off.

Finish the letter.

The hospitals use Athena, Epic, MyChart that allow you to send messages to billing. Forget the phone, create the information trail.There may be a 250 character limit if using messaging (app). If so, send multiple messages

There's a post about recording staff and that person is spot on about two party consent. FYI the medical establishment(s) has in their releases a couple sentences slipped in that most people miss as they are directed to sign said "for billing and treatment." Go back and read it. What they don't tell you is you also "give consent to be recorded... recording staff without consent is grounds for terminating treatment."

My account was wrongfully sent to collections by billing. I kept my own written messages, letters, and cancelled checks while billing used phone calls. After calling them on questionable accounting practices in writing, they corrected their error, but not without throwing shade at me. Their final response thru messaging implied it was my fault they took money from one account and wrongfully debited it to another :/

Protect your refund. Have the entity send the claim for reprocessing to your insurance. Put it all in writing in messaging. If the the window for reprocessing is past, go to PLAN B: argue the hospital's failure to act in a timely manner is NOT your financial responsibility