On the offer page it is written:
Q4. I did a prepaid recharge for Rs.100, how much cashback am I eligible for?
Customers who are eligible, will get 100% back, up to Rs.100 as part of the Exclusive Offer, by 17th Oct. Customers may also get cashback for the monthly prepaid recharges offer, which they will receive instantly. For example: customers who have done a prepaid recharge for Rs.100,
will get Rs.30 back as cashback for the monthly prepaid recharges offer instantly (refer offer terms) and will get additional Rs.100 back as cashback for the Exclusive Offer by 17th October.
Source:
https://www.amazon.in/b?ie=UTF8&node=14074947031&tag=dreamdth-21