Billing still incorrect after 8 months and 5 inquiries

I entered into a 24 month contract at a rate of R68.49. I was charged and paid R68.49 for 11 months and suddenly from the 12th month the rate changed unilaterally from R68.49 to R148.50. I lodged a inquiry 5 times and still it has not been fixed or the over charging refunded. When you enter into a 24 month agreement @ a set price, then that is what you budget for and expect to pay for the 24 month period. If I want to cancel from my side before the 24 month period, I get slapped with an cancellation fee. Why is it so difficult to get this sorted out? No compensation for all the hassle I have had so far had to resolve this Bill either. Shame on you VODACOM