How to appeal for coverage of hospital stay

Please Help w federal employees BCBS Basic (FEP blue basic of Massachusetts) Appeal

I was in the hospital for 3 nights early March and insurance is denying coverage because they think the services I was provided could be treated on 'outpatient observation status 2 night stay' which they would agree to cover. My understanding of my stay, I was told in ER that I was being admitted for observation(to be fair this was early in the morning after a sleepless night in the er and medications so I was quite out of it and don't remember a lot) but I was still unwell after 2 days so stayed 3rd night. That may have meant I was formerly admitted but I have no idea, obviously was very sick and none of this was discussed with me by either nurses or the terrible doctor I had who blamed my illness on anxiety after seeing me 2 minutes a day (my psychiatrist and GI Dr both agreed this wasnt due to anxiety when I followed up the week after) The doctor appealed first and that was denied according to this letter, which now says I have to appeal myself to BCBS first then if they reject still go to OPM. Going to request the documentation that was provided by hospital/Dr for their decision, but any other advice for how to approach this? Don't know where to start after asking for the information they based their decision on.

submitted by /u/Relative-Gazelle8056
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