Cancellation Difficulty

We have canceled out Telkom service last year November/December (2017) in the Mall of the South branch and sent the cancellation via email. Still every month Telkom deducts our account for a service we haven’t used in a year! I have logged numerous complaints and did another online cancellation in February 2018 (which a Telkom employee said it’s not on the system so it’s not canceled), even though we have returned the device to the Mall of the South branch. I have logged this issue with “The Social Media Special Force Team” to no avail. We are paying for a service we haven’t used in a year - that for some reason can’t be canceled! Who do I need to speak to, to resolve this year old cancellation?