You got great advice from Jomar and DV.
I would also add contacting the Attorney general for your state.

Yrs ago I had a problem with my health insurer, paid for by my corporation, while I was on short term disability. They would not pay for IV antibiotics my doc scripted for Lyme Disease.
I called the AG and they told me to call the legal dept at my company and say I was being denied prescribed treatment. My company called the health ins co and my treatment started the next day.

The attorney general is there to help with consumer issues and health care is a consumer issue.

Best of luck with getting this issue solved.
Shame on them for jerking you around like this.
My best,
D.