You can combine all 6 cashback deals from Freecharge.
This is best suitable for paying postpaid bills
For max benefit do it in the order-

First of all add 21 in your wallet if you don’t have wallet balance.

Now buy 15 in 15 deal for 5 rs, pay 15 rs for recharge and get 15 rs cashback. Deduction – 20 Cashback – 15

http://freecharge.com/fc/app?action=view&page=p...

Wallet Balance – 16

Second buy 12 on 12 deal for 1 rs, pay rs 1 and rs 12 from wallet. Deduction – 13, Cashback 12

http://freecharge.com/fc/app?action=view&page=p...

Wallet Balance – 15

Third buy 12 on 12 deal for 2 rs, pay rs 2 and rs 12 from wallet. Total Deduction – 14, Cashback – 12

http://freecharge.com/fc/app?action=view&page=p...

Wallet Balance – 13

Fourth buy 12 on 12 for 1 rs, pay rs 1 and rs 12 from wallet. Total Deduction – 13, Cashback – 12

http://freecharge.com/fc/app?action=view&page=p...

Wallet Balance – 12

Fifth buy 10 on 10 for 1 rs, pay rs 1 and rs 10 from wallet. Total Deduction – 11, Cashback – 10

http://freecharge.com/fc/app?action=view&page=p...

Wallet Balance – 11

Sixth buy 8 on 8 for 1 rs, pay rs 1 and rs 8 from wallet. Total Deduction – 9, Cashback – 8

http://freecharge.com/fc/app?action=view&page=p...

Wallet Balance – 10

Amount paid – 21 , Recharge Done – 69 and Cashback Left – 10

You get 79 rs for 21.