Why did you leave it on all night. If you are not intending to use it, turn it off. What was connected? The jet pack doesn't use data, what you connect to it does. I suspect one of your computers was not off and in sleep mode only. It woke up in the middle of the night and downloaded updates as it is programmed to do. Make sure you set the wifi hotspot connection on each computer as a metered connection. This tells the computer not to use data for updates and to try to minimize data use. Computers will always use much more data than phones.
Anytime your jetpack is powered on it is liable for a device to connect and consume data from the internet. Any data consumed over the Verizon network will be billed to you accordingly, regardless if you knowingly consumed it or not.
Data usage is a similar concept to your water lines. The utility company doesn't care if you or your neighbors turned on the hose. They will provide the water and bill the homeowner accordingly. Thus the best way to lower your water bill is to shut off the hose when you are done using it. Similar to finding a leaky pipe, you have to find a data leak in your environment too.
VZW will give you some basic tools to tell you how much internet is getting consumed at certain times, but VZW does not have specific information on the who, what device/app or why the data was consumed. To find out that kind of granular information you have to setup data usage monitors and capture the traffic on your own.