I have an AT&T Samsung S6 Edge Plus. My wifi will not stay off. I have disabled "always scanning" and connect to AT&T hotspot and turned wifi off. I've tried just about everything. The issue is that I drive A LOT in my job, so when I'm driving, my phone is constantly scanning and connecting and disconnecting to different wifi and it drains my battery. For instance, we were driving from New Orleans to Texas and even though I kept turning the wifi off, it kept turning back on by itself and connecting to all different wifi, the result is that even when the screen was off and not being used, it was draining about 1% battery every minute.
