Tricia,
I was denied by Empire BC/BS when I asked them to pay for a 1-level Charite ADR. Their reasoning both times (pre-certification & 1st level appeal), was that it is experimental/investigational.
In their contract with my employer, it states that they can deny coverage for any procedure that they deem is experimental/investigational. In my research for my appeal, I found that some BC/BS plans will pay for this procedure whereas others will not. The decision lies with each individual plan & some plans that will cover this procedure can turn around & reverse their decision & decide that they will no longer cover it.
As for suing your insurance company if they deny coverage after all appeals are exhausted, I'm not sure. I've been told by my OS that a class action lawsuit could be brought against an insurance company. However, who can afford to foot that bill?
You may want to check out your local department of insurance as a starting point for your research. Here's the link:
http://www.idfpr.com/DOI/Default2.asp
Hopefully this helps you out!