I have used billdesk as the payment gateway many a times for paying electricity and gas bills but have been successful in paying in a single shot just half the times.
The payment gateway specially hangs and fails for Axis bank.
Many times it gets stuck on the redirecting page and after sometime it straightaway shows session timeout suddenly.
So in short you cannot know if the payment has been done or not.
Also the speed is very slow and the entire process of logging in and conpleting the payment takes a lot of time.
I would recommend to use other gateway options if possible specially for paying utility bills like electricity etc.