This is the only way i've found to check usage properly on BSNL's stupid selfcare website.

1. Open BSNL Selfcare(only in IE)
2. Create an account with your BSNL account number
3. Login
4. Go to Service tab and select "Check Broadband Unbilled Usage details"
5. Select your phone number and click OK. If it doesn't load click OK and Cancel back and forth 3-4 times. Press the back button in IE. Click "Check Broadband Unbilled Usage details" again. This time it will take about 20 seconds. After it loads, you'll be able to check it properly.

above is for south Indian users

some other so called selfcare portals of BSNL :

west : http://selfcare.wdc.bsnl.co.in/irj/portal
north : http://selfcare.ndc.bsnl.co.in/irj/portal
east : http://selfcare.edc.bsnl.co.in/selfcare/start.swe