SANBS sends late notification of outstanding amount

I have received a number of blood transfusions this year. I now received a statement from SANBS stating that a blood transfusion in March was not paid as I am a private patient. The fact is that I am not a private patient. I have a medical aid. The problem is that 6 months have now passed which means that I cannot submut it to the medical aid anymore. But I only became aware of this issue when a statement came two days ago. I feel that I am not responsible for this. I gave my medical aid details at the hospital. The person I spoke to insists that I am now responsible for this payment. I need this to be sorted out.