You shouldn't be rejected since the FDA approved Botox for migraines on October 15, 2010.
My insurance company rejected my Botox injections on the basis that they were experimental over a year and a half ago. After going through the steps with the insurance company, I got the State to overturn the insurance company’s rejection of it.
I sent a whole bunch of information (got it from my doctor) along with a letter from the doctor stating that my migraines were over 15 days a month and that I had unsuccessfully tried a variety of daily preventative migraine medications to treat my migraines to the State Insurance Commission. You will need to have your doctor include those 2 points in their letter to the insurance company to have any chance of it being covered by insurance.
Those insurance companies will try anything to avoid payments.