Need advice for what to include in appeal

My insurance isn’t covering any of my 34k surgery bill stating the hospital I had the surgery at is out of network. I am supposed to have surgery within the dignity health network but my home hospital doesn’t have a colorectal surgeon. I found a doctor that was close to me as I needed to see him very often especially after the surgery he wanted me in office 3x a week. I live in Los Angeles so commuting any distance is an actual nightmare hence why i went with the closest speciality surgeon. He was tier 1 in my network and everything else I’ve had done by him has been completely covered, he only practices out of two hospitals that are not in network for my insurance. It never even occurred to me that my insurance would not cover this since my doctor is in network. I went out of my way to ask the hospital before my surgery if my anesthesiologist would be covered under my insurance as well and I was told yes.

Why didn’t the hospital catch this before my surgery?

I told my boss (COO of home hospital) and she never once showed concern that I was having surgery at a different hospital knowing ours doesn’t have a CRS. however we do have sister hospitals that may have a CRS I am not 100% sure and don’t know how I would even find out that info.

I’ve never had to deal with anything like this before and by being uneducated has put me in a very bad spot with this outrageous Hospital bill. Please help me I want to make my appeal as strong as possible but have no idea what I need or should include.