FYI the data usage is actually checked by a third party and is 99.99% accurate. I have verified the data usage via my netgear RAXE 300 router, and found it to be spot on.
As for what uses that much data, I can help you figure it out. Do you have alexa? Do you have security cameras/doorbell? Do you have one drive loaded on your cell phone? (Assisted someone recently in the forums and they found over 100gb daily going through their cell phone/one drive. Alexa can cause problems, and unless a certain setting is turned off, it can share your internet service with others.
IE-"Amazon Sidewalk creates a low-bandwidth network with the help of Sidewalk Bridge devices including select Echo and Ring devices. These Bridge devices share a small portion of your internet bandwidth which is pooled together to provide these services to you and your neighbors."
TV/4K can use as much as 8GB/hr.