Unauthorised Debits after contract was cancelled

I was due for an upgrade and I received and call from Mondo Rewards and they offered me a laptop, which they claimed was top of the range. When I received the laptop, it was the complete opposite of what I was promised and not even worth the contract. It was a 10-day cooling off period and returned it the very next day. They said there would only be an admin fee. I returned this laptop in October 2022 and MTN is still billing me for this laptop. I have called both Mondo and MTN many times each time and they promise that this will be cancelled. It has still not been cancelled and I'm am being billed each month for this laptop. It has been 3 months, still no credit. These guys are ******. This is costing me company time and money, as I need to keep calling them. They promised to contact me and have still not received a call. These charges are ******** as I have not agreed to this in writing and have returned the laptop. Now I have to seek legal advice to have this resolved which is more money that I need to spend. I will also go to the police station and open up a case of ***** and theft because you guys are *****ing my money. Enough is enough now.