MTN telling lies so I can make an upgrade

I went to MTN store in East Gate on the 28th of July 2015 to do an upgrade. The sales person was not truthful with the information, I was told that the previous contract will be cancelled and on august I will start paying the new contract but to my surprise they debited the bill for the previous account contrary to the information I got from the sales person. I was also not told that I will forfeit my data once I do the upgrade so I lost 4 gig that I had. when I called customer care line I was told that I need to go back to the store to sort it out because the people at the store misinformed me. When I went to the store I was told to call customer care line to sort it out so I am being sent back and forth now I don't k know what to do