BILLED WRONG MEDICAL AID

In Jan this year my daughter fell ill and was admitted to vincent Pollotti hospital. AT the emergency desk I personally gave all my medical aid details to the receptionist/clerk. When she was admitted I again gave all my details to the hospital. I belong to Old mUtual medicla aid and have been a member for the last three years.all my bills were paid accordingly except for the er consulting who somehow used my old medical aid details on there system(best ed). after months they contacted me and expects me to make payment because it is too late for them to resubmit to my medical aid. I said I refuse to pay the account as everything was already paid and its not my fault there people billed the wrong account.I phones them numerous to have the account checked but they never give me feedback and keep sending me warning letters.I sent an email on November the 13th and never got a reply. I followed up on NOv 25th and spoke to the manager Betwell who said hel check why I was wrongly billed and respond with feedback,never did, and now today I get another letter telling me they officially handing me over as I refused to pay, Please help!