Arnab2085, I have never used metered broadband and think it is an abomination — but I understand that some users must resort to it. I don’t know why your usage is so high when you’re basically not using your connection.
You didn’t mention who your provider is — or if the usage meter you referred to is a stand-alone application or just some static list you can access in a browser.
You might wish to download another usage meter and compare the usage to your provider’s usage meter. Here one possible open-source meter:
Hopefully, someone else with more experience will add a comment or improve this answer. Good luck and let us know what happens.