I think I solved this:
I went to app permissions, then the first one by me was Facebook app, when in, I found a checked option "could change WiFi network" I disabled it. Then checked any other app permissions, it was strange, the was none option like this....only by FB. One day, passed, I was out then out it looks like the was no WiFi, but coming back home I saw I have WiFi turned on by itself again. Try it! And enjoy..