My computer started doing that a year or so ago. I checked all of my settings and worked on it for a few months and finally had to do a factory restore and it has been fine ever since. I don't know what was going on in the background but I suspect it was a virus. Otherwise be sure all the pages you use like FB have automatic videos turned off. Chrome has some settings to turn them off as well for some pages but you need to do it inside some sites also.
If you haven't called in or emailed us yet, could you send a quick email over to firstname.lastname@example.org? Please include your account information and/or a phone number that's tied to your account. By doing this, we can look up your account and see where this data is going to. Like Deb suggested above, there are many things that can go on in the background without your knowledge that could cause a lot of your data to be used. We can take a look at it and see if we can pinpoint what the problem is.
the thing is watch 2 movies on Netflix and your data is gone watch any video and your data is gone you all need to get with the times ur service sucks and you over charge i pay $70 a month for a service and get get 27 GB at 3 mbps when I find out I can get 300 mbps no cap for 79.00 per mo. keep up the greed and you will be an 8088