hdavis71,
Data usage reflects the amount of data used by online activities, not the amount of time spent online. If you have any devices online even while you are away from home, they can receive updates automatically. I suggest checking your Anti-Virus settings and check for any programs running in the background automatic operating system updates.
Sending a tech to the house would not determine your individual data usage. The Data Usage Meter is the best way to check your Data Usage. You may also use the Cox App: https://www.cox.com/residential/learn/cox-app.html
I recommend checking daily, keeping in mind the usage updates up to 24 hours later.