Wifi using power even if it off
Configure as shown . These are for Marshmallow and may differ on your device 


Settings → Google → Services → Location → 3-dot menu → Scanning → Wi-Fi scanning &rarr; Disable


(As confirmed by OP on Nougat Settings  → Location → Scanning → Wi-Fi scanning &rarr; Disable )


Settings → Wi-Fi → 3-dot menu → Advanced → Keep Wi-Fi on during sleep &rarr; Never
Settings → Wi-Fi → 3-dot menu → Advanced → Network notification &rarr; Disable


This should fix the problem in all likelihood