Question about what to do after external review failed

Last July I went into the emergency room due to 48 hours of pain that resulted in my gall bladder needing to be removed. Because it was late at night and the pain hadn’t let up for so long, the doctor recommended that I stay over night because that would mean that I could get into surgery first thing in the morning. It was heavily implied to my husband and me that if I went home for the night, it might be up to a week before they could get me in for surgery.

Due to this recommendation, I stayed, had the surgery the next morning and everything has healed up fine. However, BCBS denied the claim saying that I didn’t qualify for the inpatient stay. My understanding is that they didn’t think I was in bad enough shape due to the fact that I could hold down food and wasn’t vomiting.

I appealed the rejection, when that was denied, a request for an external appeal was submitted, but I just found out that they have upheld Blue Cross’s denial. I am looking at an 18k bill that I am not in a position to pay and am feeling very overwhelmed right now. The surgery took place in Utah.

What are the option I have going forward. I’ve seen that filing suit is a possibility, but I have no clue where to start with that or what that would cost.

Thank you to anyone who helps.