Gems (Government Employees Medical Scheme) refusing to approve medication

Gems (Government Employees Medical Scheme) refuse to change my wife's current medication Orencia.The problem with Orencia is that it's always a struggle to get the medication, always a different excuse why they cannot deliver. I use to be on Enbrel and never had a problem, but due to side effects I could not stay on Enbrel. Since the change from Enbrel to Orencia I have been struggling for months now to get Orencia.The doctor suggested to move me to another medication that will be more available, but GEMS refuse. This is a problem, because my biological medication is the only thing that controls and keeps me as a Rheumatoid arthritis patient standing. If someone can assist that will be very much appreciated.