To check the bsnl broadband bandwidth details go to http://selfcare.sdc.bsnl.co.in/ You have to register first and then you can go there and see the details...
One you register and login there is home menu next to it, you can find service menu.
Click on the service menu and from there choose "Check My Broadband Unbilled Usage Details"
Then enter the dates from which you want to see the bandwidth details for.
The bandwidth is reported in KB convert that into GB and you get your details. Also make sure to see the last date of the bandwidth report so that you know its up to date. Sometimes the report is a day old.
Sometimes this report will under maintenance.
Then you can just dial 1500 from your broadband phone line. Once you give your phone details choose billing details. And from there check the unbilled usage. It tells you the amount that is unbilled if its says 5500 Rs that 55 GB. It costs 1000 Rs for 10 GB.
So these are the two ways you can check your bandwidth.