Overcharged for by R1900 with no explaination

I am at the point of screaming and crying at the billing department at MTN. For the last two month I have been overcharged by MTN with R214. I went into the walk in centre at Century City and within a few minutes they corrected it and indiacted that I will be credited with the amount on my next statement and that this wont happen again. They have checked all my details on my account and everything is as it should be.<br> <br> I just received my MTN statement for July and they are now overcharging me by R1900!!! that will be coming off my account by the end of the month. Now my only option is to go back to the MTN walk in centre on Saturday (which also happens to be my birthday) and yell at them again. This however wont stop the R1900 overcharge from being debited from my account.<br> <br> How am I going to afford this. I dont have that amount of money and if I dont pay it my account goes into arrears which I have to again pay for. I have a child that I support and am preparing for the arrival of my new born baby.