Disppointing service from Discovery Medical Aid

My dad has Discovery Keycare. It was disclosed at the time of application that he is diabetic and had diabetic foot ulcers previously. he now needs to go for debridement of his big toe since he has a ulcer under the big toe nail, which requires removing the toe nail as well when debriding toe. Process is tomorrow but discovery is rejecting claim even thou the doctor sent a letter of motivation. they saying it general and not covered. but how can they not cover for something that is caused by being diabetic. dad's foot is so swollen. we can't leave it like this, it might become septic. Really disappointed with the service from Discovery,