Is there a free adsl (broadband) usage tracker i ca download? if so, what is the isp?

My recorded usage, according to bt, has suddenly shot up from about 2gb monthly to over 11 gb! i have not been doing anythging different to normal. i do not download music, films etc.
Answer
Maybe they r charging u for some1 elses usage. our phone bill was like way high last month so we called the phone poeple and they said since uve changed your number, so weve charged u for som1 elses usage. so phone them up and ask