Let down and **** to by Discovery health AGAIN

My daughter went into theatre on 19/06/2018 for a dental procedure. We were given preauthorization and were told that we just had to pay a copayment at the hospital, which we did. Now we are being told by Discovery that they do not cover basic dentistry. Please can Discovery tell me how they approve Something and even give us a preauthorization code, (Authorisation code : ********** 932) now say this??? Please can someone advise on the method to take Discovery on legally, as this is the THIRD time they have given us issues for paying when we have claimed for pmbs. What other medical aid options can anyone advise? Because Discovery is an ********* company that is only concerned about filling their own pockets and giving their clients lies and false promises!