Discovery's incompetence

Discovery retail medical scheme, which we are members of, we went in to the dentist to do an extraction, before anything could be done, we asked for funds availability to be checked, it was confirmed R1181 was available on my sons name, twice this was confirmed with two different references. So we went ahead with the procedure once this was confirmed. A few days later claim is rejected, funds depleted. Now we are liable for R1004 to the dentist. Due to discovery's incompetence we are now indebted. I want it fixed.