You can gather evidence by taking a screenshot of your data usage meter every day. You could then show them how much you're using daily/weekly to refute the charges. You'd have to use 42 GB per DAY for 30 days to reach your limit of 1280 GB. Click on "Past daily" and it will show how much you used each day for the last 30 days.
And if your daily usage seems way too high, maybe a neighbor is stealing your wifi bandwidth. Can you log on to your router to see everything that's connected, and account for every device?
I've been binge-watching 8 seasons of Homeland with my 30 day free trial of Showtime on my Firestick and my data usage is not all that high. 700 GB is my all time high record of usage. Normally it's less than 600 GB per month. My daily usage is less than 20 GB per day.
