Telkom sucks big time

In 2016 i took up a Telkom data contract through a call center agent that had called me. I have never used the data on the sim card because their network coverage was so bad. I had no signal at all so i decided to cancel the subscription. I called in and informed them that i would like to cancel and a cancellation form was sent to me. I filled in the form and sent it back. However Telkom is still debiting money from my account even though i have called in so many times informing them that i had cancelled their services. I have been told that they did receive my cancellation form but they are still debiting my account. I am so sick of this because they just refuse to cancel this useless service.