Updated the iTunes but keeps asking it needs the latest version iTunes

I have a locked iPhone 6s and want to unlock it using iTunes. It asked me to update to the latest version. Well, I did update and it is in the latest version now. But when I plug my phone and click Update or Restore, it keeps warning "To update your iphone it needs the latest version of iTunes." What a non-sense? This is the only way to unlock my phone. The Find my iPhone method doesn't work to unlock because it needs to be connected to internet. But I can't connect a locked phone to internet. What a non-sense? I need a help to unlock my iPhone 6s.