Hello. Same issue happened to me in July and in August.
I supposedly used 30x my usual usage within 3 days of my plan, and I was at work 2 of those 3 days. When I chatted VZ customer service, there was no response or explanation. So, effective July 4th I stopped using my long-ago paid-in-full hot spot and switched to another carrier for computer use.
For the 3 days my plan has been in effect for August (8/3 - 8/6), my unlimited calls and texts phone usage shows <0.01GB of use. However, when I checked my plan use online, my data usage shows that I have used nearly all of the 8 GB allowed on my plan and that I am close to going over...in 3 days and ZERO use of their data plan. No answer when I called customer service. They have just lost another customer...and I will continue to share my experience with others.