Worst service provider ever

Done my upgrade at mtn cresta last year October, since then I have not had peace due to the incompetence of mtn staff!!! After taking out a sim only contract for 299 I get debited for 828 for 3 months , went to mtn and only the store who upgraded you can assist which makes no sense! Called the other store and the ladies are disgustingly rude and at cresta there's never a manager the manager is always on leave or sick so that doesn't help any complaints! Eventually the lady THULI at cresta agrees to help and says no my account will go in a positive when they sort out the amount I'm being debited for. And now for the month of February I owe MTN money after being debited almost triple for 3 months. Called the store this morning and their attitude is absolutely disgusting and they are rude and left me on hold for 15mins! Please mtn help