Yes, this is a copy of Jio, but even Jio did not give 100% Cashback. They are just playing with words. The cashback of Rs 400 is over a period of 8 months, not within a single month. So it is not 100% Cashback. For each Rs 50 worth of cashback, you have to pay Rs 399 each month.
Hence Total payment over 8 months = 8 X 399 = Rs 3192
Total Cashback over 8 months = 8 X Rs 50 = Rs 400
Actual Cashback received against total payment done = 12.5%. Airtel's MyAirtel App itself gives Rs 15 Cashback on Rs 100 payment. Thats a straight 15% Cashback month-on-month. And you can use this offer multiple times for multiple payments of Rs 100.
I always observed this, hence this offer shown is an eyewash.