How can my Jetpack 5510L go through 35GB in a matter of hours overnight with no active devices connected?

[golfmeister]

I woke up to 18 data overage text/email messages - many of them like 2 minutes apart. The Mifi was frozen on the "fully charged - remove from power supply" screen.  I had to remove the battery to restart it.

Verizon tech support changed my plan to a 40gb plan and said they "would help me out" with the $250 additional charges, but this was clearly a device malfunction.

Has anyone else experienced this issue?