They'll only send you the past month, and apparently I used up 270GB last month, which my router completely disagrees with.
They are most likely talking complete hog wash. Sure, if you are constantly downloading and maxing out your line then this will slow down your internet, but if you have 10 kids all watching HD YouTube and playing xbox online, that's about 4-5mbps per kid. Now if they were all downloading the latest call of duty update...
What is your contracted speed?
What speed are you getting? If it's less than half your contracted speed you can complain.