Contract upgrade without permission

I have had a LTE service from Telkom. Near the ending of such contract Telkom upgraded my contract without my permission, I cancelled my contract telephonically. Now they charge me on a monthly basis for these costs and denying that I have ever cancelled. On a phone call to the mobile call center I was told that my number has been allocated to some one else. But they will fix it and proceed to cancellation process. but till date nothing. You can not get a contract without you confirming for a debit order to go off. Since April no debit orders was ordered from my account, only the billing amount rising up. Numerous phone calls to Telkom and no positive outcome. The call center attendants service are as bad as Telkom's services.