Disgusted by the fact that amount balances are always accumulating even after paying, how?!

My experience with Vodacom has been pathetic.I have been paying for my contract more than the phone costs. Evetytime there's an amount to pay when I call in the agents will tell me there is an additional amount to pay. I was told 6 months ago by a Consultant named Karabo that my outstanding balance was 8k over 6 months I have paid it with an arrangement that has been made and that was the only amount owing. After paying that balance there is suddenly an amount of R500.00 outstanding. I cannot understand how everytime I call in there is always an amount t added on and Vodacom has the best excuses. I have complained about the service I have asked for Confirmation emails to be sent to me agents will agree to sending u emails with confirmations but nothing has ever come through. And now I am listed on ITC for an outstanding balance that has been paid up. Something needs to be done or I will sue Vodacom this is disgusting!