I'm also facing the same issues with BSNL, The gateway assigns IPV6 address to my devices but I can't even send a ping through IPV6. It used to work earlier and it's not working from past 2-3 months. It depends upon your local exchange and how they respond to the complaints. I made complaints for IPV6 and higher loaded latency and the Divisional Manager responded to me that if I don't like the service, I should terminate the connection. I mean if I had any other option why would anyone opt for BSNL.