I would also suggest contacting your local representative and indicating on your letter that a copy is going there. You could also send a copy to members of the Congressional Multiple Sclerosis Caucus. With luck, your representative is on the caucus. (Maybe she or he will join!)
http://msactivist.blogspot.com/2008/04/ ... aucus.html
On the left, if you scroll down, you'll see the members as of 2008.
This is exactly the type of issue that needs to come to their attention.
Each local MS Society chapter should have staff who deals with health care/insurance advocacy as well, and you might get some good advice there as well. I don't know if you've ever looked to that route for assistance. They know all about insurance denial and appeals!
If you don't know who to call, look at the NMSS home page and call the MS Navigator.
And just for being obvious -- save every single piece of paper, take notes of every conversation and name and time, and keep your dignity and your confidence!
I remember it actually took more than a year and several appeals to get BCBS to reimburse me for the home birth of my son. But we did eventually get it done. Hang in there!