Useless service I want my refund

Mtn has been deducting my account for over 6 months now after I told them that the modem they sent me does not work. I had the modem for a month still didn't work. Cakles them and told me to take it to the store. Went to compus square store wasting my time and petrol to be told I have to call service center. Called service center again was told to take it to the mtn store. Went back to comlus square. When I got there this agent told me there is nothing he can do I should call service center. I left the moden and everything sith them last year with my number and to date I have not received a call nothing all they do is deducting my account. I want my refund in full and cancel this ****** contract. Useless. I have had mtn for about 15 years.