Airtel — sim conversion from postpaid to prepaid

Address:

Dehradun, Uttarakhand, 248001

I want to convert my airtle sim form postpaid to prepaid as the per month bill keeps on increasing every month. Whereas the bill for per month in airtle is coming around 450/- as if you compare Jio is providing services for 399/-rs for 3 months. Seems like airtle is charging triple the amount with no extra features.