I started using freecharge and it worked for me. Their new website design however has few glitches with the javascript. And that makes the payment form to not work some of the time. So I moved to paytm for few weeks. It is simple and it can be used to for recharge too. System is not slow like freecharge. Also the payment is instant and you get invoice in mail too. There is also mobikwik, their app is good and you can also use their wallet for online transactions. Apart from these options bank app can be used for the mobile recharge or the bill payment. And finally the app of the telecom operator itself. For example, Airtel money, Vodafone, TataIndicom etc have their own dedicated apps and website for the recharge and bill payment feature.