No. I do this for living. I have a palo firewall behind with only home macs allowed ontop not to mention my wireshark runs constant. I can read this like the f-ing matrix. No don't have a tin foil but we live in a f-ed up world.
What would it cost to try it? You're assuming your controls are working properly and haven't been compromised. But you're seeing higher than expected data usage. How do you know there's been no unauthorized use?
Are you sure no one has social engineered your Wi-Fi password?
I do this for living.
How hard could it be for you to change a password?
You could also have a device that's continuing to use data when it's not actively in use. An example might be a streaming service that continues accumulating data usage if it's not signed out after you've finished viewing.