I'm not happy with MTN service for my contract

I'm having contracts with MTN I'm not happy with the way they are treating my account,first im having a problem I upgraded last year I took laptops I was supposed to get 4GB day n 4GB night but I'm not getting that,I've been calling and going to the store but no one is willing to help me,then now I cancelled my two lines because the contract ended they promised that they won't load data on those lines to my surprise they loaded data now I must pay this week for those two line, when I go to the store they are telling me that I must call head office as in store they can't do anything, when I called head office they are telling me the thing they can offer me is data to continue with my contract,how can I continue with the contract while I can't afford and worse part I'm not happy with MTN service, please help as this is starting to annoying me as really if I can't pay you will be the first one blacklisting me but now you can't help me while I can still pay