My wifi autoconnects even though i have turned off everything possible in the settings
Do you have any app that auto connects wifi, like tasker or Samsung's new application called 'Good Lock'? Because Good Lock creates routines and by default if it gets in some predefined location than it starts wifi and some other services. 
(sorry, I don't know if this can be termed as answer or not. But my reputation is low so I cannot comment and I just thought Good lock can be creating confusion)