I can see you're having some trouble getting your iPhone 6S updated. It's very important to have the latest software on your device and you've come to the right place for help. It sounds like you've tried some really good steps to resolve this but to no avail. No worries, I have some info that may help.
- Just to be sure, when you tried to update using iTunes on a computer, did you get an error message? If so, what did it say?
- Were you using the latest version of iTunes?
- Did you test this on more than one computer?
Update the iOS on your iPhone, iPad, or iPod touch
If you see error messages in iTunes or need more space to update
Get help if you see error messages while updating your device with iTunes. Or if you need more space for an update, you can delete content from your device manually.
Let me know and we'll work on getting you updated together.