Discovery Health reneges on approved, life-saving cancer treatment

I received approval from Discovery 3 days ago for Herceptin, a life-saving, preventative treatment for aggressive Her2+ breast cancer.

I just received a call from Discovery to say, sorry, we made a mistake based on your tier level, we are retracting approval and treatment.

I received this approval in writing. Surely an ethical business would not deny such treatment after having issued approval? Besides the physical consequences of not receiving this treatment is the emotional and psychological impact on myself and my family, who Discovery gave hope to for effective treatment of my cancer, only to renege on their word.