I have got many emails saying that an error code 13 has been occurred while recharging through Airtel prepaid cards. So i have decided to find a solution, at at last i am presenting it here!
Normally you need to type *121*3#<16 digit recharge code> but due to some problems some users don't get the recharge done.
For those who want this solution type *120*<16 digit recharge code>#
This code will work for sure, as i tried it asking the customer care! Have a great day................ !