Medihelp refusal to pay chronic medication

About 2 years ago my husband was diagnosed with heart failure. He only had 16% heart function. After seeing multiple doctors and specialist's we finally got to one of the top heart specialists in South Africa. He told us he will fix his heart without needing a transplant. And he sure did with a few trial and error medications we finally got one that worked, Vymada. But this medication is quite expensive, we tried getting our medical aid to pay for this medication as it is chronic and is keeping my husband alive and has bettered his heart function to 45%. Medihelp refuses to pay even half of this medication even after all the reference letters from all the doctors and specialist's. I'm at my ropes end with this and need help please.