bad service

I did an uprade with mtn on the 8th of July 2015 and i was told my contract was a top up and i will only be charged connection fee, end of July my bill was 513 and i thought maybe its that connection fee, to ny suprise end of August i paid R1542,10, i then called mtn to find out whay was going and they told me about data that were not limited, they told me the store should have told me about the unlimited data but the consultant that did my uprade didnot explain anything to me about data limit usage, i then asked for the limit to be set and i went to the shop to talk to consultant who did my uprade, to my suprise she knew nothing about data usage limit as well and promised to look at the.matter. End of September i got a bill of R2741.98, i could afford to pay such an amount, i called mtn again and explained the whole situation, they told me to go to tje store and speak with manager, i have been in that store from october until now nothing is happening i keep explaining the same thing to the manager, he is always sending emails to his boss who does not as well as a result my phone is suspended and no one is doing anything about my complain at the store.