Accounting does not follow up with Medical Aid

Lancet has serious accounting issues. Accounting department is incapable of contacting me in person, despite my requesting numerous times. They can't find a payment done by my medical aid and they are harassing me now, even sending another company for collections. This is absurd as I have already sent my medical aid statement stating account is settled. Allegedly Lancet cannot discuss anything with the medical aid, entity which they have business relations and receive payments from. Terrible service as the account department hides behind the call centre and simply can't be reached. There is simply no interest whatsoever from Lancet to solve this situation, apart from sending me invoices and threats to mess with my credit history.