Unable to get my sim cancelled by Telkom

I have been trying to Cancel my sim held by Telkom since January 2017. I have been into the Telkom stores in Canalwalk on at least 3 occassions, sent the cancellation notice to their cancellation dept and still Telkom are taking off the monthly installments. I have spoken to countless agents at Telkom and have been assured too many times to remember that this would be sorted out. I would absolutely never recommend Telkom to anyone. The service has been by far the worst I have ever had from any company. I will give it another try this week but will not hold my breath, not sure where to go with this. I would like this account cancelled and the installments reimbursed. But I suppose there is more chance of it raining in Cape Town.