Billed for incorrect testing!

I just received a bill from Pathcare for a shocking amount of R709. My doctor advised to do a full blood test and explained that the only test I would be charged for from Pathcare was a vitamin D test which was around R100 and my medical aid would cover the rest of the costs, which I agreed upon. Forwarding to a few weeks later, I've been made aware that Pathcare tried to claim an amount of R709 which was rejected by my medical aid for a HIV PCR Qualitive test (overly expensive HIV test counting all cells). At no stage did I request nor agree to do this test, I didn't even know what it was until I done some research to gain understanding of what this was and I certainly didn't require it. I DO NOT have the means to cover this cost and won't pay it! I demand an investigation into this matter, whether it be mistake from my doctor or your lab I should not be held liable for someone else's mistake! I don't know if this was mixed up with the standard HIV test or not but please get this resolved ASAP!