Late Authorisation passing the blame to patient

My son had an accident at school , we rushed him to Mediclic Meulmed in Pretoria, and he was treated. A week later they started calling with the invoice, only to find out they processed things so quickly they used the wrong codes and claimed under the wrong department—my son had a dental injury. The medical aid then charged them for a late authorization because they had to resubmit. Months later, they have been trying make me pay for their mistake!! Meulmed you should be ashamed of yourself!!