WiFi gone in less than a week!

I am supposed to receive 20 gigs of data each month on my WiFi profile. 10 day and 10 night. This month I only received 8 gig day data (don’t even get me started on the night data). I’ve done only a few updates and now all the data is gone. Please explain to me how much data these updates take and how 8 gigs of data can be gone in less than a week. And why was I only given 8 gigs to begin with? I used to do a lot more with the 10 gigs, even watched Netflix and it would last at least 3 weeks. So what is the problem now?