most likely you will need to contact verizon for specifics. sometimes your internet service goes down at night. maybe contact them to see if it were during the specific nights you had issues. just because you got the email at night don't mean that is when the data was being used.
check and make sure you have the google play store setting for wifi only. go into your data settings and see what app is using a lot of data and when the data is being used.
This happens all the time. I'm at home and in my wifi and the 4g icon on the phone starts flickering. It happens to my. Wife's phone too also an s7
A few times in the middle of the night we ended up. Getting emails from Verizon notifying us about just reaching 75% data for The month.... How the hell could we do that while we're sleeping....

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