Apparently Facebook is breaking the rules and regulations of Play Store, however why Google haven't block it from Play Store. It seems like Google likes to bully individual apps developer or small companies by blocking their apps once they break a single freaking rule, but Google allow huge companies like Facebook to break the privacy rules?
Anyway, here is how to disable the Facebook apps auto update completely.
1. Disable auto update in Play Store apps [hey, don't assume you did that, because ass-u-me ;-) ]
2. While till in Play Store apps, look at another auto update button on the Facebook apps
-> Play Store -> "My apps and games" -> "INSTALLED" -> (optional: sort by Aphabetical) -> Facebook -> 3 dots on top right corner -> un-check "Enable auto update"
3. Disable the auto update in Facebook apps (yeah, inside the apps)
-> 3 bars on top right corner -> "Settings & Privacy" -> Settings -> "Media and Contacts" -> "App Updates" -> disable the "Auto-Update Facebook" button
4. Done, happy.
I have only the guide for Android, hopefully it is similar for iOS. Good luck disabling auto-update by Facebook apps.
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source: writing on my own after learn from google search result