Where does all my bandwidth go?

I got like most people a pleasant surprise to download Windows 10 for free but wonder how free it really was. To start when I downloaded my \free"version I ended up using something like 7.5 GB where I was warned it may take something like 2.6 GB. Keeping in mind bandwidth in this country is pretty expensive. I buy 10 GB a month and this month sofar and its only the 3rd of the month and somehow have used almost 4 GB. I also notice that windows 10 does not give an option to turn off auto updates which I have noticed in the past can be hundreds of MB's at a time. I suspect this is where my bandwidth is being used and question the legality of the process. I am sure there are thousands more out there having the same problem."""