Non payment of service provider

My son had a operation 04/06/2014 with authorization number ***3. On 19/06/2014 he had to go back for the new cast and on 14/08/2014 for the follow up. This was all part of the operation. Now after numerous attempts to get the payment from Discovery i have to turn to Hellopeter an d social media. The Dr said that we should come back on these dates for the check ups but according to Discovery i needed to get authorization for these check ups that is part of the operation. Please advise me on what to do as none of my attempts to resolve this matter was successful.