Some modems have a built-in data counter. See if you have one.
I have a beetel 450TC3 Model +wifi Installed directly to the phone line of BSNL via a splitter, One line for Landline and One for modem , thats it.
Yup. I transfer a lot of data between phone and computer using BitTorrent Sync. Even Android bandwidth meter cannot differentiate between local and Internet traffic on wifi.By local you mean data shared through local area network like files or prints and other stuff ???