We have password protected wifi, of course. But this month I have noticed that usage for one week used half of the data I pay for. That's not normal. How can I find out what is going on? Can I log into my router? If so, how do I do that?
You can view connected devices (devices logged in to this router using data) by viewing the FAQ for this and following the instructions to log in to the admin page @ Verizon 4G LTE Broadband Router FAQs | Verizon Wireless
Once logged in go to the Connected Devices tab to see what is connected.