Billed for cancelled contract

Sometime in February I bought a 7.5GB promo contract that comes with a wifi device. Then the 1st day I received the device the data was depleted, because it was the middle of the month I let it slide. I waited for the following month. It was the same story, data depleted with 1 day. I then I called customer service, the lady could not explain it and because it was somehow within cooling period she then app**** for cancellation. But they billed me a cancellation fee, to which it was debited from my bank account. Only to find out that my Telkom account is still open, and i have been invoiced after the cancellation. I cancelled the debit order, and then after several month my Telkom account went to arrears and they handed me to their collection department. About 5 different people one after another and I explain the same thing, and it also confuses them. Somehow they credited me my cancellation then billed me for all the other months after the cancellation, at the moment my Telkom account has credit but they still debit me on a monthly basis for data I do not even use, because it has been cancelled. The matter has since been escalated from 02 June 2015 until now.