Unfortunately you will have to appeal and if that fails, appeal again and threaten to report them to your state's insurance commissioner. It is an approved standard of care for crohns disease and they pretty much cannot legally deny you that. If they do, then force them to approve humira or cimzia which will be somewhat cheaper for them (and you) and tell them they have no choice in the matter. If you are forced to undergo surgery because of their refusal to approve the treatment, tell them you will SUE them for damages, lost wages, and emotional harm. Make sure when you make that phone call you get the name of the person you are talking to, the call record number, and tell them you want the call recorded. If they say they cannot record the call (A boldfaced lie since all companies record their calls to protect themselves) then tell them you are recording the call and do so. Make sure you tell them you are recording the call to prevent any legal issues with if it is a one party or two party state for recording calls.
From there you just have to call and call and call and call and call. Also, get your doctors office to call and if necessary spend $100 for an hour of a lawyer's time and have them draft a letter and call as well. You will get the medication approved, if you follow a plan like this, it will just take time. Their strategy is deny first, approve only the persistent second. I hope this "guide" helps you some. We have all (mostly) been through this before and persistence is the key to getting approval. Also, ask for supervisors and managers when you call. If the first line call center says they cannot do that, tell them they can and they will if they value their job, then get their name and employee id number. If they refuse, call back and ask the new person for the information on the person you just talked to (it is in their system guaranteed) and write it down then explain you need a supervisor to report an issue with a call center employee. That will get you through usually.
If you have to, take a day and call them nonstop talking to different people every hour, then do it the next day and day after.