Retracting Authorisation after it was given

I am now at my wits end with trying to speak to anyone that is able to assist me without telling me this is not their department or their issue, however for me it is a massive issue.

I was given authorisation for a procedure - ***6 - open cholecystectomy by Umvuzo and the operation was done on the 13th of November. The hospital has now started calling me everyday as Umvuzo are refusing to pay the hospital bill and they have been told that I am now liable for the bill, their words were:

"kindly communicate directly with fund as they indicated procedure is a scheme exclusion. Case is closed and pt will be held liable for the shortfall on the account."

This message was sent by - Tshuma, Lucia from the e-mail address - ***

So now I am liable for an ZAR88 000.00 bill that was actually authorised by the medical aid, and no one has ever heard of Lucia Tshuma, they say she does not work for Umvuzo and no one can find her, I have left messages for Elaine de Waal who is the manager of authorisations team, however she does not call back, and this is now a matter of urgency as I am meant to go back to theatre next week in order to remove something in me that cannot stay in me and if I cannot afford the 88 000 they say I already owe them how am I meant to afford another day?