Frustrated by Telkom

I took a contract with Telkom in September 2014. The contract ended in September 2016. I did not extend the contract, instead I requested the contract to be terminated. I did this numerous times telephonically ( as I took the contract telephonically), however, at a later stage I was advised to complete a cancellation form and email it. I did that around August 2017. To this date Telkom is still debiting my account on a monthly basis. I have visited telkom shops several times and all efforts have proved to be in vain. The SIM card is not in use since June 2018, however, Telkom is still billing me for subscription and usage to this date.