deactivation of sim card

Location/place: mumbai

Name of company/service: vodafone

first of all vodafone called me and convinced me to convert to postpaid from prepaid service. but after that i was charged very very heftily, turns out they hadn’t enabled the proper schemes.
now i called these people to discontinue postpaid and turn it back to prepaid. so they said it cant be done on call and i have to go the vodafone gallery, and today i see they simply deactivated my sim ! this is ridiculous