Cancellation instruction not processed

Send cancellation instruction in January for a contract that expired last year. The instruction was not processed and I followed up with several calls (holding on every time for over a half an hour) and emails. The debit order is still going of which I reverse every month - the following month Telkom just doubles the debit order. This morning I got billed for 3 months - which I just reversed again - every time at my cost!!!!!This is unacceptable! What can be done to get this resolved as I tried all avenues now!