Being charged for a canceled contract by MTN

On the 16th February 2023 MTN send me a faulty laptop in a new contract. I took the laptop together with the sim card back to Mall of The North on the 17th February. On the 20th February I canceled the contract because Mondo misrepresented the facts regarding the price and my existing contracts. After speaking to several agents from MTN I was assured that the contract was canceled and the number was removed from my name. On the 18th March Yesterday I was told by MTN Mall of The North that I owe them R12000 for the laptop I returned and the contract I have canceled. To make matters worse when I enquired with customer care the agent sent me the current invoice showing the charges of the canceled contract and the laptop I returned. How can I be charged for a line that was removed under my name and the laptop I returned within 7 days which is a cooling period as guaranteed by the Consumer Protection Act.