Discovery key care plus shortfall cost me thousands

I have been with discovery health since my new job and had a medical aid before that. Never had any issues until I had to pay for my own medication and procedures, I had a fall down the stairs and was taken to hospital where the specialist requested a CT scan via GP, the medical aid didn't want to pay, I had another cone CT scan and before going to the procedure I called the medical aid and got a preauthorization but now I'm sitting with an bill of R2684.60 because it's not in their chain. There is no other Dr's that does VEMP test or Cone CT scans in SA that's in their chain. So now I'm sitting with massive bills that I never had before taking this medical aid, the spokes person for Discovery tells me I should think of taking a higher plan, what's the use of this current plan then? Why implement a plan that won't work? Or put you in a catch 22 situation.