Pre-Authorized Out of Network Surgery and Hospital Stay, Still Waiting for Claim Processing

In late June, I had to do a surgery. The surgeon was in my network (Anthem/BC EPO in California), but both hospitals in which he has privileges were out of network. His office applied for pre-authorization and obtained one for the surgery and 2 days of hospital stay. The pre-authorization letter about the hospital stay explicitly stated that even though this hospital is out of network, this stay will be treated as in network as long as I stay during the time they approved and do the procedure they approved.
The hospital kept me for 2 days and 2 nights, and released me on the morning of the third day. During the second day, they asked me to sign a form that stated that I understand I'm not being admitted but I'm there for "observation". I have no family, so being alone in the hospital and not being able to do much research after the surgery, I just signed it.

As of today, the claim has been denied, stating that they are waiting for further information from the doctor.

My questions are:
1) Can they deny the surgery and the 2 days of the hospital stay, which they explicitly deemed medically necessary?
2) Can they deny the second night of the hospital stay? From what I understand now, insurance pre-authorization for 2 days isn't 2 periods of 24 hours. I don't know if the hospital obtained any further authorization while I was there and I wasn't in any situation to find out. I don't know if they were required to obtain one per California and Federal law either. What was the hospital's obligation and what is the insurance's obligation per California and Federal law?

3) How can I speed up the processing of this claim so that it has a favorable resolution? The large hospital bill hanging above my neck has caused so much stress and anxiety in me that I could do without.
TYIA

submitted by /u/backwardentropy
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