Telkom continues to debit me long after I had terminated the contract

I had a 24 month contract with Telkom which expired in Feb 2020. Seeing that Telkom was still deducting my money after the contract had expired, I cancelled the contract on 28th May 2020. They still continue to deduct money from my account till today. When I contact them, they always promise to contact me back but they never do. On top of that, they charge ridiculous interest when I reverse the debit order. This is pathetic.