Billing on cancelled and ended contract

I called on the 18/08/2023 to cancel my contract as it had come to an end. spoke to Tebogo and she assured that the policy will be cancelled effective 18 Sept 2023. to my surprise is saw a debit order of the amount higher than what I was paying when the contract was still in place. I need this to be fixed and be refunded what is owed to me. I'm supposed to be paying for only one line as of end of September.