Mtn bad service

I had a month to month plan with them since 2023, Cancelled it in January and returned the mtn router to the store and i was billed twice the amount in feb, Now i have a credit amount which they need to refund me its been 3 weeks now, without this been resolved, all you get is emails saying that this had been attended to. Their connection is terrible, as well as their customers service, what a waste of my time, my money and energy.