Hello,
Sadly, this is a fairly typical problem. Have you tried having your doctor write them a letter listing all the other preventive treatments that have failed for you?
What was the reason BC/BS gave you for not covering it. Sometimes, the reason they give is that it's not FDA approved for Migraine prevention. If that was their reason, take a look at Migraine, Medications, and Insurance Companies. There's information there on what has worked for some people.
Please keep us posted?
Teri