There could be a few things that could have caused it. Most cases if it's a dramatic and sudden spike like that an update is usually the culprit. If you email me at firstname.lastname@example.org with your account information I can review it for you and see what happened.
One new player in the "I'll drain your data" game is Nividia's newest video card driver.
One Hughesnet user reported that his Geforce driver used 1 GB of data in just a couple days.
The "telemetry" landscape is changing quickly and not for the better.
Some details and solutions for this "drain" can be found here: