Airtel — Prepaid online topup payment receipt not issued

Address:	Vellore, Tamil Nadu
Website:	www.airtel.in/myaccount#

I had done an online topup for my airtel prepaid mobile for Rs 300. As in other networks like aircel and Tata docomo, I expected an online payment receipt popping up after the transaction was over. But on the contrary, no such receipt appeared, though the transaction was successful. As it is an official mobile, I requested for a payment receipt atleast to my email ID. But the response was that they have no provision for the same and cannot issue any receipt. Are they not legally bound to provide a receipt for any transaction?