Reporting it to customer service so they have it documented is critical. I worked with a second level Verizon person who is going to call me back after my billing cycle. I can download the dates/times where the big chucks hit and we'll see where it ends up, but if not fixed I may need to go to another phone and/or carrier.
On the Verizon Wireless website, log in to My Verizon and you'll see your device listed. The middle section is My Usage, and at the bottom of that is usage details. Click on that and the next page will show voice, text and data. Scroll down to data and click view data details and it will show the amount of data used at specific times.
This specific detail is only available on the website. Not the mobile app.