Overcharging - Several calls,store visits,promises

In short MTN overcharged me two months - several calls,store visits, promises that someone will call me back and 4 months later still sitting with the same issue. Frustrated is not even the word anymore, this is just straight forward terrible service. This got to a point now where I'm going to involve my lawyer. At this stage Im advising every single one to stay away from MTN. Can someone please assist before I take next steps. Thanks for understanding my frustrations.