Billed on Medical Aid Rate and not cash rate

Hi <br> <br> i had allergy tests done for my son and i had told the person assisting me at lancet that i had no saving in my medical and i wanted to pay cash. They then insisted that i go to the pediatrician because i wont know what to test for which is an additional cost just to him( the pediatrician) to fill out the test form for me. I then get a bill that states that the medical aid rejected my bill and that i am liable which is not a problem until i noted that i was billed using the medical aid rate. I asked that my bill be revised to cash which should be cheaper but i was told this cannot be done due to the fact that i am held liable for the rejected bill. I cannot be liable to pay so much money R3600 is a lot and i am a single mother how is this fair. Help me understand the fairness of this ?