My broadband plan/speed not changed i dont know what is happening ?

I am from kerala circle and my plan is unlimited 675 plan but my speed is not daily plan basis . i have getting whole 150gb for a month with 10mbps speed and 2mbps beyond . actually my broadband is not changed to daily limit system i dont know why my plan service is Base-HS-H-UPG-10MB-150G-2MB-M .i have no daily limits. its funny that bsnl is giving me 150GB at 10mbps and 2mbps beyond plan for me . actually its a good thing but its not good when i use to download big files in a month . previous month i contacted to bsnl kerala cgm office but they said they are in a bug .today again speed exhausted message and i have getting only 2mbps below . i dont know what is the exact problem . anyone happening same situation ?