Has anyone experienced something like this? My MiFi (Jetpack 6620L) apparently used hundreds of megabytes of data even though (as far as I can tell) no device was connected to it.
My data usage log on the Verizon website show the following information below:

The 45.39 MB used at 12:45 PM on 4/5 looks normal. What is astonishing is the 349.25 MB at 6:57 AM on 4/6 and thereafter.
I left my MiFi device in the office yesterday (4/5), with the USB charger connected. It's configured to allow only one device to connect to it. The password is private (no one else knows it), and I only use a specific laptop to connect to it. I brought that laptop home with me, so there is absolutely no possibility that the device was being used in the background to sync iCloud videos, update my laptop's software, or any of that sort.
Furthermore, I was asleep at 6:57 AM, and my office building is empty around that time. This is a building full of software engineer geeks in California; no one comes in at 7 AM. Yet the logs show that 349.25 MB was used around that time!
There is simply no explanation for this. I talked to Verizon, and they told me that according to their records, the device was indeed using that data. They refunded me the $15 that I was charged for passing my data limit (which was nice of them), but that doesn't explain how this happened, and I definitely don't want it to happen again.
Has anyone seen something like this?