They wont tell you what they wont cover until you have already done the procedure

I would like to issue a complaint regarding discovery medical aid. Policy holder had a spinal cord operation at the net care cuyler hospital on the 3rd November. The pre-authorisation was done with discovery and they sent the first confirmation on the 2nd November and another on the day of the operation, however on the 4th November they sent another email saying they will not be covering the full hospital stay bcz the hospital is not in their spinal cord procedure network hospital. This is information they should have advised on the first pre approval so the account holder can get the opportunity to change the procedures to a different hospital which the insurance would cover fully. However, the policy holder was sent an email on the 4th telling her they will only pay 80% of the stay. Leaving the policyholder with the R31000 bill. I have tried to contact discovery numerous times to dispute however they still maintain the claim is valid.