Once again paying more than what my contract says

I am really getting upset and very irritated and frustrated with Vodacom now!!! this month they have deducted R313.00 off my account where it is suppose to be R260.00. Last month was R410 because of their mistakes and this is going on now for the 3rd time in 1 year.<br> <br> Please can you explain to me why I have to pay more for my contract with you guys when it is suppose to be R260.00 per month. Every month I get a surprise on my billing account, you know what some people do not get increases at companies like me so how am I suppose to survive if you guys bill me all the time incorrectly.<br> <br> I want answers now from management and I really want to cancel my contact with immediate effect I cannot go on like this and sure you guys will come up with some stupid excuse like always