Keep deducting money after contract was canceled

Telemarketer falsely sells a wifi modem with LTI telkom modem data. Says the product will work where I live. Then it only works on roaming. SO the 2 GB telkom mobile data included in the package is useless. Return it. They reverse the first payments deducted. Then from there on every month deducts more than R 2000 (two thousand rand) from my account. Been lodging complaints and reversing the deductions. They keep deducting. If it bounces, they just deduct again. All they keep saying is they are busy with the case, or the they did not remove the account. The package was not even R 500 a month. So I don't know where they got the amount of more than R 2000 they are deducting.