Airtel — postpaid to prepaid conflict

Address:

Vishrantwadi, 411015

I bought an airtel sim on 22nd march 2019. When i bought the sim i was told the sim itself is postpaid and i cannot get it prepaid.
I said i would like to change it prepaid as soon as possible. They said you can do it after 30 days and/or the first bill cycle.
After that i went on 30th of apr to change to prepaid. They changed their tone and said it takes 90 days to switch from postpaid to prepaid.
I called customer care (198) and now customer care said it takes 30 days.

So i had customer care speak to the airtel employee in the airtel store near me and they could not resolve the conflict. So customer care asked me to wait for 48 hours to resolve this problem. I called again on the 8th and went to the store. Same conflict.

It's now been 10 days and there is no resolution.
I called 198 again just a few minutes ago. And still nothing.
My question.

1) is it true that some numbers are reserved for postpaid only? And cannot be bought for a prepaid connection or was i fooled?

2) how long is the lock-in period for postpaid to prepaid migration?

3) i am being billed for services i am currently not using. I have waiting for your resolution for 10 days now. That means i just wasted rs.100 out of my postpaid bill just in waiting. You are ripping me off while making me wait.
Do something useful.