Overpaid for teats

I would like someone to get in touch because all I get is generic emails without an explanation. I went for blood tests within the network, Ampath then charges me full amount saying it’s not covered. I query this with Discovery stating that I was only meant to be charged a specific portion, and that the rest is neither payable by Discovery or me, the thing is I had already paid in full, so who exactly must give me a refund of what I overpaid? I messaged both Ampath and Discovery and neither is taking responsibility.