Nighthawk LTE Hotspot Data Usage thief?

We have two LTE Mobile Hotspot Routers. One we stream TV, etc, #2 no streaming except occasional radio.  The #2 location is consistently the huge user of data for our two different location accounts.  The only wireless active when we leave is a Honeywell thermostat and they tell me that only uses 85MB per month. Everything else is unplugged. My account restarted yesterday at location #2 with no streaming, internet access only and it has already used 2.5 GB!  How can I trace what is using this data?  Thank you for any direction