TELKOM BILLING AFTER CANCELLATION

I took a LTE contract with Telkom in June this year, when I took the contract I asked them to check if there will be coverage. When I received the unit it had signal but it was very slow. I took a 20meg uncapped contract but I could not even watch Netflix without connecting any other device. I contacted them 10 days after I received the unit to make sure it does not get better. They informed me I had to cancel within 7 days. I said its fine I will pay for the month and they should come and pick up the unit. They only picked up the device in SEPTEMBER after I phoned and logged complaints with them about 4-5 times promising me to cancel it every time. However were at the end of October now and they're still billing me. When I chatted to them today they couldn't tell me when it was cancelled, when I asked questions of why they haven't cancelled it, they rudely cut me off, I started a new chat and the same thing happened again. I would love if someone can assist as I don't have the device and they confirmed that the sim is not in use. BUT still they bill me. I've reversed every debit order but I get charged bank charges every time.