Breach of Trust and Contract by MTN.

This is regarding breach of contract by MTN, where they have been overcharging me from last 6 months. I got myself samsung tabs3 from MTN, contract was suppose to be 518 ZAR, they have however been charging me 800 for the same, even after multiple complaints they give no resolution. Seems like now I need to goto small claims court, this is pathetic from MTN.