Month to Month does not exist with MTN bad service

I took up a month to month home fibre internet with a router with mtn and my billing started on the 15th of May 2025 so my billing was running from the 15th to the 15th every month.On the 5th of December 2025 I cancelled the contract and handed the device in at Ferndale on republic MTN store and the service was bad as the lady didnt want to take in the device because she said its a lot of work. Ref: *** I got that reference.On the 15th of December my account got debited for the month of 15 December to 15th of January 2026 of which I queried with MTN why I got debited for the next month when I dont have the device to even use the internet I received this reference Reference MTN BO*** that it will be sorted. On the 15th of January another debit came out of my account and I am so frustrated why they keep debit my account when account was cancelled.