Contract cancellation

I’ve been trying to cancel my contract with Mondo since November 2020. I was told to return the wifi router to any MTN store after I wasn’t told that it was a home router. I did so but my account is still being debited and every time I call I’m being taken from pillar to post. I’ve been reversing debit orders from MTN because I can’t be paying for a device I’m not using. I’ve had it with Mondo! If I could rate them a -5 I would!