Vodafone India — change of plan

Address:

Assam, Kamrup Metropolitan, Assam, 781007

My vodafone postpaid plan was for 99 rental per month.
When i checked my bill today it was 700.
On enquiry i found they have changed my plan to 299 without my confirmation.
I got have gone for prepaid if their plan is closed.
How can they change my plan to 299 without my confirmation.
This is really frustrating and even on asking they said their plan is closed so they could have stooped the services then i would have taken necessary decision.
But no they changed it at their own will without my confirmation.