Bad Attitude/Rude concerning overcharges!

Despite having explained to Vodacom that I would like to keep within specified budget of calls (barring the line altogether at R300) I have been overcharged on several occasions. I then reverted to my top up account which I deemed a safer option so as to prevent excessive billing. Still I find that I am being overcharged on the account which is absurd since it is a \top up account"! I have even been billed right up to the end of July (invoice received a week ago!) when we had just about got into the month and one wonders how is the bill calculated in advance... even though it is a 'top up\"". Tried explaining this to Zanele Mabena who was very rude & redundant in going over the same irrelevant details repeatedly despite what I was trying to explain. Clearly she wasn't interested in hearing me and behaved as though she was wearing blinkers. She then blurted"