DOTEL/R/2019/50697

I am an Idea prepared telecom service user since 2 years, but from past 2 -3 months my sim is not working so I visited Vodafone/Idea Store at my neaby locality for about 5 times for the same problem to provide me a new sim card of same number (i.e. 7039991676). But the representatives says they can provide sim of same number but only on postpaid not on prepaid.
But what i want is only prepaid.
if i had prepaid connection than why they ask me to take postpaid.