I'm having this same issue too, on a new Samsung Galaxy J2, in Australia, September 2018.
-I have auto updates turned off in the google play store.
-I have made sure auto update is unchecked on each individual app in the google play store.
-I have turned off auto updates in the Galaxy Apps store too.
Even after all this, apps keep on automatically updating. This is very annoying because for days I've been trying to download a large game, 1.73GB in size, and every time an app automatically updates, it stops the game from downloading and the download has to start from the beginning every time.
Please help!
Google/Samsung, this is not good enough, FIX IT!