Contract cancelled but Cell C is still debiting my account

I called Cell C in July 2020 requesting cancellation of my contract. The agent that I spoke to told me that the last day of my contract will be on 27 August 2020. In September 2020 I realized that the contract is still active, I then called Cell C to find out what was happening and I was told that the contract was never cancelled and was promised it will be cancelled immediately. A few days later i made a follow up and was told it was cancelled. Now Cell C is debiting my account every month for September 2020 bill and I don't understand why I'm expected to pay a bill for September bill when I had cancelled my contract in July. It is not my fault Cell C staff chose not to cancel my contract in August as requested. I lodged a complaint with Cell C and the agents that I spoke to were not helpful at all and I'm tired of calling Cell C and reversing the debit order.