Billing Errors and Bad service

If I could give them 0 stars I would. They have messed up my billing almost three months in a row. They keep putting a block on my contract before the billing date, quoting arrears amounts of almost double and not more than double what I am suppose to pay. My latest invoice says there is only R199 due to be paid on the 15th, but I am getting an email from a William on the credit department with no invoice, just a typed out email saying I owe R528 and that I need to make payment to their account and email proof of payment back. Last month when I went to the branch they said I was in credit and only needed to pay in R75 for the month. The next day they blocked my account saying I was in arrears, the balance of what I paid in and what I was suppose to be in "arrears" of, came to more than my monthly bill. I paid it and put in a query because I need the data for the work I do. But now this month, an account that was suppose have been paid up, "or how else would they have reconnected me if I supposedly had a balance" and is only suppose to be R199 a month, all of a sudden has an arrears of R528. I just don't get where these figures are coming from, and they never call you back when you do eventually get through to them after hours of dialing different number because they cant just put you through to the right department. I am very disappointed with them, me an my mother have been using Mtn for years, but have been canceling our contracts one at a time due to bad service. This is the last straw and we will be canceling this last contract with them as well.