postpaid vs prepaid

I ported my Idea number to JIO prepaid plan. My initial plan was to use INR 149 Plan, that give 4 GB data. I did some calculations. 149/28 = INR 5.32 Per day. I purchased pan INR 399/- for 70 days as cost is same, but 70 GB data with this plan. 399/70 = INR 5.7 per day I looked at post paid...