Fully disable Spotlight Search I would like to know if there is any way to disable Spotlight Search, even when an user goes to Settings -> Spotlight Search, and change the options there.

That's mainly because anyone could still search in Spotlight only by going to Settings -> Spotlight and enabling the search on the web. I do know that you can set it so you can apply filters, but they are not successfull at what I need. (Yes, I know also that Safari can be restricted under "Restrictions", but I am only talking about Spotlight)

I would need something like "Spotlight Search" under "Restrictions", so I can turn it off completely, so any user can't enable the Internet search again.

That's like a little bug for anyone who want to be fully protected for mature/adult content. (I want to have my own filter, not what Apple says that is good)

PS. Currently I am with iOS 10.X in an iPhone SE. There's a video from youtube here that explains how to disable Settings app. That would be great, but that workaround only work in older versions of iOS.
First, reboot into recovery by restarting your Mac while holding down Cmd+R. From Utilities, select Terminal and enter the following command to disable System Integrity Protection.

csrutil disable

To check if it is already disabled, run csrutil status.

Now, just run this: 

mv /System/Library/CoreServices/Search.bundle /System/Library/CoreServices/Search_disabled.bundle


Then restart your Mac and Spotlight will be completely disabled.
Don't forget to re-enable System Integrity Protection once your are done.