So, it can be very difficult to tell what would be covered. They are not regulated on this issue. I recommend that you never take no for an answer from your insurance company. You should first call them up and ask them why. If they tell you it's because the treatment is experimental or not medically necessary, you should tell them that you would like to appeal.
All health plans have some formal process for appealing a denied claim.
You should get your doctor to help you assemble all of the information about why you need the care. If they uphold their own denial then you should call your state insurance commissioner's office for help. In a growing number of states you can appeal your health claim denial to an independent medical expert and the decision is binding. The independent medical experts look at your case and at the criteria that the health plan used to make its decision. They look at your medical records and decide what they think, in their expert opinion, you should get.