Pay Me Back Dis-chem Nicolway

I have been trying for ages to get Discovery Nicolway to pay me back what they owe me. I went to their pharmacy to get my meds, and paid cash. Then I got a claim notice from my medical aid mentioning that they had also paid. So, they got paid twice for the same transaction. I have sent emails trying to fix it. They never reply. I think they are trying to rely on the passage of time to make me forget that they essentially took money from both me, and the medical aid, for one transaction. And I don't see how that is legal or even ethical. I have been patient.