Contract cancellation at mtn

I bought a contract of unlimited wifi and it came with a router at mtn over the fown in January, I called in to ask how do i set it up but the was a problem with the router and i called in and told them that. They sent me to my nearest mtn and the person there said i must return it back, ever since then mtn is not sending me the address or send courier to come fetch it, but they are billing me for wifi that I am not even using cause their router never worked. I am a very patient person because I have been calling them to fix the router or send a new one and they keep on saying that they sent an email to the person who is suppose to take care of my problem but nothing. Last week I called to cancel and they also said they sent an email to the relevant person to take care of my cancelation till now, today is Friday and my problem is still unattended. I never want anything to do with mtn