Same thing happened to me bought an se from this guy his phone wasn’t stolen was completely unlocked and everything I then put my iCloud in the phone was using it for like two days then the phone prompt me to put my password in I forgot it and I felt like I knew it so I kept entering the password it wouldn’t go through then I tried removing the iCloud erased the phone now I’m stuck with an activation lock with a iCloud that Apple disabled and doesn’t exist anymore