Someone is controlling my iphone 6s plus

Your phone has a hardware fault.

What you describe is the classic signs of a short in the digitizer.

Take it in for service.

prettydarkkin_gurl Said:

“Someone is controlling my iphone 6s plus: My iPhone 6s plus is acting like someone/something is controlling it. I have restarted it a lot of times but it's no use, whoever is doing this is accessing my apps, and enabling, disabling, accepting, and declining stuff. It also send random text messages to people(that don't make sense)[...]”

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Restore your iPhone to your iOS.

Start by backing your iPhone:

You would connect this to your computer and back it up, through use of iTunes. Go Here: How to back up your iPhone, iPad, and iPod touch - Apple Support

Then, Restore the iPhone:

Restoring software on your iPhone (iOS Device), deletes all your information and settings, but it doesn’t erase it.  So, delete it all. But backup your iPhone, as instructed above, prior to this restoration. Go Here: Restore your iOS or iPadOS device in iTunes on PC - Apple Support.

Sounds like a failing touch screen to me.

Is it possible that your Apple ID used by other family members along with you?

Axel F.