@Pranab bro gets all good offers from Freecharge. Not valid on my account.
Here is a generic FreeCharge offer for all that I found:
Recharge/PayBill for Rs 15 and get Rs 10 Cashback.
Promocode: FC10
Works even if you have used FC10 for the previous offer a couple of months ago.
It's because I stopped using FC for almost 3-4 years.
Currently I'm not using MobiKwik for more than a year after they started the nonsensical supercash.