Contract cancelled at end of term but they still debit me

Telkom contract expired and gave notice on 17 May 2021 that I will not reniew. Recieved email confirmation. Phoned 10 days later. Never canceled and they will do immediately. Debit order went off again end May. Phoned ..promised it will be canceled. 25 June debit order went off again. How is this possible. Phone the call center. They can't help. How? Why do I need to pay for something I have cancelled and given notice that I will not renew. I want a refund.