I just bought a "factory unlocked" galaxy note 8 on ebay. Was supposed to be new and looks like it was "open box" new, which is fine. however, as soon as I started it up, I had a T-Mobile splash screen. I'm thinking this is a dead give away that it is not unlocked. But I have no experience in this subject. Any pointers? My plan is to replace a 6 year old LG Optimus on my AT&T network. Should I return this?