MTN bills me for nothing.

I had a cellphone contract which ended on 17 July 2024. This contract included a device as well as some data and minutes. I was advised to give 30 days notice of cancelation for wishing to cancel this contract. I contacted MTN on 14 June 2024, to give my 30 days notice of cancelation with effect from 17 July 2024- last payment date 01 August 2024 as it is paid in arrears. To my surprise on 01 September 2024 a debit order goes through for MTN. I called into the contact centre on 04 September to enquire. The consultant - Lihle- advised that it was a device fee and I received an allocation- which I did not. She was trying to transfer me to the allocations department and then billing department and after 20 minutes the line disconnected. Firstly, how can I be billed for a cancelled contract. I received no data or minutes to be billed for. Secondly, if my contract was cancelled with effect from 17 July 2024, why would you give me an allocation. I want a refund for the money deducted on 01 September 2024, as their deduction was ilegal.