Can't cancel unauthorized debit

Telkom has been billing me even though the sim to my router is no longer on my account. No consultant at any Telkom shop can help and I am forever being referred to the call Centre that doesn't help either. There seems to be no management team and this all seems like ghost management. I am tired of reversing payments, this will cause me to get blacklisted. They just take your money when they feel like it and much more than what you're supposed to pay. This is my last resort before I open a case.