I really don’t understand why such bad ratings for a renowned website? Many operators and banks have tie-ups with them. It was formed in 2000 quite before those "start ups"!
Vodafone use bill desk application for post paid billing, and that is when I came to know about this service. Seems like people who have give negative reviews don’t have an Idea about the company or the website.
They have partners with many Electricity, Telecom, DTH, Insurance utility, You can go through this page to know more:- https://billdesk.com/partners.htm
So they in fact are leaders in payment industry. I feel really secure when doing transaction through this application. But they need to market their products more.