Vodafone — Change my postpaid connection to prepaid connection.

Today I visited your service center Uttarpara branch with a request to change my postpaid connection to prepaid connection. The representative of your Uttarpara office told me to come after one week as it will take one week time to process. But after coming back to my home I found one message and also email stated therein that my post paid plan for Rs.399 to Rs.499 as per my request. I don't come to understand why this type of change has been taken place. Please look into the matter and arrange to change my postpaid connection to prepaid connection w.e.f. today.