I bought a Vizio 70 inchClass 4K Ultra HD LED LCD TV in April.
Same thing was happening to me. I would turn it off then like 3-5 minutes later it'd just cut back on. Sometimes it'd cut back on like two or three times before it finally would stay off. It was mad annoying.
Around August is when it finally just stopped. I didn't do anything special, it just finally stopped.
So I wish I had an answer as to how to stop it, but I don't. I used to and still do suspect it was one of the HDMI cables or ports that was making it cut on randomly. I still kinda do. But it seems to be a Vizio problem too in general.
Wish I had an answer on how to stop it but if you're patient enough, yours will possibly eventually stop randomly cutting on like mine finally did.