Dissapointed

I took a month to month router with MTN which they were debiting from my account on a monthly base, then I later cancelled my subscription with them and they instructed me to return the router to one of their shops, I did so in November I dropped it at MTN shop in Meadowdale and was given a ref as proof of receiving, Now Mtn claims I owe them R3000 for the Router which I returned one of the consulted say they charged me for it and ive been calling and calling but no one seems to help, instead I get one story after the other. All I needed was for them to clear the 3k as they have their router back and clear my name.