Useless Provider treating customers unfairly

I am very angry beyond frustrated at the serve I am receiving from MTN after faithfully paying my contract and ready to upgrade they allow an outsourced company to do an upgrade on my profile , a wrong upgrade giving me a phone which I dnt even know it's name. After returning the phone no one from them calls me ,to give n update when I follow up no seems to know what to do! MTN can be very useless when they choose to.3 weeks no one has resolved my query.