MTN month-to-month contract cancellation

I have been trying to cancel my MTN month to month LTE contract for the past month. My call either gets cut when transferred or when I email I am asked to call. Finally when I get through, I am then told to return the router to the store first. There is also a 20 day notice period - so I am not sure how its going to work as I wont have a router withing this period so I will be paying for not using the LTE for that period??