Admin not doing her job well and as a results this is costing me

I made a co payment as the Medical aid short paid my account so I had to cover the balance and now I am unable to claim from my gap cover because the Admin lady by the name of Marina from the Doctors room made a mistake by putting the incorrect amount of which she claims that she put the correct one whereas according to Bonitas she is the one who billed incorrectly, I believe what Bonitas is saying because when we started with this query she indicated that I did not mention to them that I have a gap cover so that makes me believe that she is the one who is wrong and not Bonitas,to make matters worse dhe keep on saying she sent the right documents and when I call Bonitas they say there is nothing on their system,I went to Doctors office last week and Marina gave me copies of the documents that she sent to Bonitas unfortunately she didnt show me the mail sent she just gave me copies and she promised to give me feedback on Wednesday which is yesterday, I called Bonitas this morning and I spoke to Mihloti who told me that she cannot see anything on the system except the call that was made on the 18th,she also explained to me as to what needs to be done,I then called Marina since she promised to get back me of which she never did and all she did was to hang up,I really don't know what to do now because its clear to me that she doesn't want to help me I mean how do you work with customers and treat them like that,all I want is for her to fix the mess that she created because this is costing me as I keep on calling her office and Bonitas since the beginning of the month.