Still Billed but I have cancelled the service over 3months ago.

I have cancelled my service in April. Service was discontinued 4 May. I have been billed ever since. I want money owed tome to be refunded and I want to stop receiving invoices for a service I do not have. I do not want to be blacklisted for owing money because i don't! I don't have service Telkom. Telkom has promised to sort this out but it is still ongoing.