I experienced the same thing one month. Seems there has been a bit of "partnering" between YouTube (Google) and FB. As was stated above, need to ensure that the settings to allow video is off. I had to go to the extent of completely logging out of FB to make sure that the videos weren't running in the background. Haven't had a 12+ GB (18+GB on the girlfriend's) bill on my 4GB plan since. Logging out is the best failsafe to ensure that the video services aren't reactivated without you're knowledge.