Struggles with Canceling an MTN Month-to-Month uncapped WiFi Router Contract: A Frustrating Experience

I purchased an uncapped WiFi router in January, but the network performance was poor, despite being told it could support six devices. I returned it after a month and was given a cancellation letter with instructions to provide a number when contacting online support. However, when I called, they said the store needed to email them after checking the router. After a month, they attempted to debit me, claiming the cancellation wasn't finalized. I was directed back and forth between the store and online support, which has now dragged on for over three months, negatively impacting my credit score. I'm perplexed as to why there's a lack of communication and resolution, especially considering I have a phone contract with them that I've been paying without issue. Has anyone successfully canceled an MTN month-to-month router contract?