I bought an iPhone 6s through AT&T and fully paid it off last month. I'm trying to switch over to another service, but whenever I enter a new sim, it says that it's not compatible with my phone and that it needs to be unlocked. So I did what anyone else would do and headed over to the AT&T website to try to unlock it. I entered in my IMEI and it said that my device is active on another account. Prior to this I made sure that my device was deactivated and everything already so I don't know what it's trying to tell me. I can't call customer support because i no longer have service with AT&T and I can't use any other service.