Bad Service

My contract was about to end. I went in store to ask for a upgrade,no one ever tell me about the upgrade charges. The device of my upgrade i app**** was not available in store because they were waiting for stock to came. I ask if i can wait because i wanted that device, and i also ask the consultant they if my contract are going to stay as my old one, or I'm going to be charge a more than i was paying on my old contract. The consultant they call they customer service and was inform that I will still be paying what i have paid on my old contract till they can get my new device for me for my new contract. On the billing for September they charges me more that they say i was going to pay. I went back to Mtn to ask about that billing and they inform me they will sort it out. the next month is was the same. I was yet again inform that all are going to be sorted, I also ask if they are going to put me on bad credit and the manager inform me that if will not happen. I have paid every month my contract and never did a skip a month, but my new contract was block and i could do nothing with it.(the new device a received October 2014) In January 2015 mtn put me on bad credit, i want to cancel