MTN

I just want to know how does MTN WORK? i had a router for about three months then i decided to cancel it because i was not happy with the service i was been overcharged, on 26 february i returned the router to clearwater store for cancellation and i was told to pay amount of 849.00. I was given form to email to mtn the IRM***8 which i did for cancellation up until this day the router is not cancel , i am told stories when i check my credit score on experian MTN says i owe them 5000..for what i don't know ..MTN IS THE WORST NETWORK AND EVEN THEIR SERVICE. Shirley sithole she told me how much to pay but after i sent her proof of payment she no longer want to help me. am even seeking legal advice because what is happening is really not fair.