Medical aid unfair approval

We have been with Discovery for many years, my husband has been struggling with autoimmune diseas past 4 years he has seen many doctos, been in hospital more than you can count and had countless test and has tried numerous drugs to try and help him. There is a medication that has shown promise for people with his condition and his doctor believes this is his best option however Discovery keeps rejecting the meds approval for him we also know people with same condition that gets the meds and they are also with discovery how is this fair. He has even had chemo still his condition gets worse this meds can help. Discovery They said we must upgrade to higher plan type that covers the meds we have done that still rejection with only comment he doesnt meet criteria but when our doctor tries to follow up on what os the criteria she gets no answer. We have 6werk old baby that needs her Daddy why will discovery not give him a fighting chance to get better we believe this meds his best shot.