Unhappy customer :(

Hi ,I'm a customer that is so disappointed and angry, have upgraded my Data option with MTN service provider last month, the agreement was to give me monthly data of 2G but however I'm getting 250MB when I call the call Centre they keep on giving me different days to call back with no resolution and I will be billed for something that I'm not even using which is very unfair as i was mislead and no one is willing to assist :(