Unauthorized debit orders

My experience with telkom has been quite horrible to say the least. My contract ended with telkom last year september. My name is Dilshaad Sayed. An agent from telkom called me to ask if i would like to continue this contract. i declined, as all calls are recorded, this can be tracked and listened to. In october, they debited my account again. i then called in where i was requested to fill out a cancellation form and send it to ********** ********** which i did numerous times. Telkom has continued to debit my account on a monthly basis even though i have not used that sim card since last year september. When i called them to ask about what the money was for, the agent could not answer me. I then went into my bank to create a stop order in December. In January they did not debit but now randomly in February they have changed their reference and debited R436.00 on the 20 february 2018. How do i stop this? i have even went into the telkom stores for help, no one has assisted me watsover. Telkom is the worst company in the history of all telecoms. please help! i have incurred costs of reversals and this month was unable to reverse the debit order in time! I need my money back and to not have this issue any more.