Changed contract without permission or notificatio

I have a yaclick system, last month Vox decided to take me off my current plan , put me on a 1mb line plan which doubled in monthly premium, with not a quarter of the benifits??? I have phoned twice, emailed 3 times and went to a store where I was told they cannot help me because they cannot see my contract on the system??? <br> How can i pay R650 the one month and R1163.71 the next, without prior consent/warning or any notification? <br> <br>