Data Usage

There are a number of things that can cause excess data usage. If you do a lot of streaming media, and you have a 4K tv, that can use as much as 8gb per Hr.  If you have Amazon Echo/Dot/Alexa, they can periodically go into a listen/transmit loop where every noise it picks up it tries to send it to Amazon for translation as if you are giving commands. I had a friend recently remove all of his amazon equipment, (Dot's Echo's, etc), and his usage dropped over 800gb a month. Sometimes gaming can use a lot of data, it depends on the gaming system and game. Also, change your SSID and WPA key, there is always a possibility that a neighbor is stealing WiFi from you and is using your data. Make sure you are using either WPA2 or WPA3. Using anything else makes it simple for a hacker to get in. If you are using WEP, even I can crack it in less than 30 seconds, (my fingers are getting slow, I used to be able to do it in 15). 

Scan all your devices and verify the software, One forum user had a similar issue to yours, found out he installed one drive on his tablet and it was uploading over 100gb daily. So, check all your devices and ensure they are not doing something similar, as well as running anti virus and anti MALWARE scans on all your devices.