Any ideas on getting care for my rare illness?

A couple of years ago, I was diagnosed with a rare autoimmune illness that requires the attention of a liver specialist. My insurance (BlueCross BlueShield CareFirst– obtained through the healthcare marketplace and sponsored by my employer) doesn't have any liver specialists that are in-network, meaning the cost of care is impossible for me. I have confirmed this with an agent at BlueCross.

When I contacted my insurance about this, they told me to have my chosen specialist fill out a Single Case Agreement form in order for me to pay in-network prices for care, since it is medically necessary. Sounds really good!

Since then, the insurance company has been dodging me. When I faxed them the Single Case form, they said it didn't shown up. I emailed them a PDF of the documents, but they said they aren't able to open the file. They told me to have the doctor call a specific number, but when she did, they did not know what a "single case agreement" was, and claimed that she had contacted the wrong department.

So I spoke to a health advocate that my workplace provides. The weird thing is, when he asked BlueCross about my doctor, BC told him that the doctor I want to see is in-network, because the hospital she works in is in-network! This is after a year of them telling me she is not in-network (and a $450 bill from a single visit).

The health advocate wants me to find out the tax information of the doctor so that he can figure out what's going on but I have no idea how to do that.