ER Visit. Hospital Says I was Admitted?

I just got a letter from my insurance denying a claim from an ER visit. The reason for denial was that it was deemed medically unnecessary. It was claimed as inpatient.

I went to the ER thinking I was having a heart attack. After a few hours on an ER bed, I hadn’t seen anyone except the nurse since I the initial Dr checkup. I asked the nurse what was going on. He said that they were going to admit me for observations overnight. I told him that I wanted to go home. The Dr came in and we discussed my leaving against Dr’s orders. I signed a form and went home.

I looked at the ER visit in my medical app. The notes from the other Dr state that they were contacted by the ER Dr for admission, but that I had left before being evaluated by them.

I didn’t think much about it until I got the insurance denial letter 4 months later.

I think the hospital may be charging for inpatient care that I did not receive? I never left the ED, but there are charges for a semi private room and more that add up to a very large amount. Note that I have not received a bill yet.

If you made it this far, thank you, and what should I do?