Request for the termination of Telkom Contract

I took a two years cellophane contract with Telkom in 2018 and it was supposed to be ending in 2020 December. However they are still debiting an amount of R100 every month. I have sent them an email and wrote on their Twitter account requesting them to terminate my contract with them but still they are deducting. I have stopped they’re debit order in July and in August they deducted R400 and some change on my account. In September I also stopped their debit order however they sent me an email informing me that they will deduct R400 this month October.

Kindly assist me by terminating my contract with Telkom.