Follow this OP: http://www.myce.com/news/how-to-uninstall-kb3035583-the-windows-10-downloader-for-windows-7-and-8-1-75681/
You have to "Hide" it from the security update/program updates depending on what OS you have (Win 7 or 8.1) after doing the above so it wont download it again.
I'm keeping Win 8.1 on my laptop and will get Win 10 when I build my new PC next year.
Sucks you lost your data (data caps suck ;x) but ya its annoying that it automatically downloads it in the background lol.
Close call for me then, I was about to install that KB3035583 updte when I noticed your post and proceeded to hide the update while choosing the optional ones. I won't be using 10 till I see some more changes and perf gains and an eventual price tag next year since I don't want to lose my Win 7 key and do plan on upgrading some of my parts which win 10 will definitely disagree with and lock me out of.
"Six days have passed, on the seventh, I will render myself to a day of rest and to contemplate...what is to be"