Airtel is probably aiming at getting free use of funds for 7-10 days. Its online recharge failed twice after deducting the amount from the bank account.
Your bank account gets debited but your phone doesn’t get recharge. When queried, Airtel says it will be credited back to your account within 7-10 working days. This happened twice for me - once with ICICI Bank and second time with Federal Bank.
Very convenient ploy by Airtel to get interest-free credit. Do not use online recharge function with airtel. Go to your friendly neighbourhood mobile shops for recharging your phone.