No cover for a medical condition

I have a very over active Thyroid that makes me ill but Discovery do not cover for this condition. My T4 is 54 and it should be between 10-20. Severe Depression, High blood pressure, weight loss, heart pulsations, hands tremors, memory loss, nervousness, anxiety, trouble sleeping, muscle weakness, etc is the symptoms I have due to this hyperthyroidism. Treatment for this condition is radio active treatment or surgery. No other treatment is available for this condition but the treatment is not available on Discovery's PMB. Hypothyroidism is available but not hyperthyroidism. The symptoms are very similar . My specialist completed the PMB form but funding was not approved. How can a medical aid not cover medical conditions especially as serios as this. Untreated hyperthyroidism cause very serious medical conditions like kidney failure, liver failure, high blood pressure can damage the heart, etc. My blood pressure was 120/80 but with this condition 160/90 but for Discovery this is not a serious enough condition to cover? I've lost 10kg in 3 months and I'm now 15kg under my ideal weight and still losing weight. But for Discovery Health this is nothing because they don't cover this!!!