The most I've ever used is around 700GB, otherwise it's 500-600 GB. I cancelled Directv and have been streaming movies from Prime all day everyday, plus my PC pretty much stays online all day, not to mention my Ring cams are always active. Are you streaming 4k resolution or something?
I tried out their data calculator and you can stream almost 14 hours of HD content per day without breaking past the data limit, but of course this might depend on how many days in the monthly billing cycle they use. They might use 31 days one month (causing you to go over the limit, and 30 days for another billing cycle, leaving you under the limit. I suggest bookmarking the link to your data usage and check it everyday.
Maybe someone is stealing your bandwidth. It's not unheard of. Google it for how to find out.
Meanwhile, change your passwords on everything connected such as your wifi router and your computer. If someone nearby hacked your wifi router, they could be using up your data plan. Then start monitoring your data usage often, to see if changing your passwords made a difference.
