If that's the right info then It's not even signing in from the psn app. So they locked your account globally that means. Not good. You should call Sony and ask to talk to manager but I dont think they will help you. Don't admit to sending those messages if they say anything just say your lil cousin be using it sometimes but you know nothing of that.
There was a video of some dude who was like lvl 20 trophy he lost all his dlc, downloaded games and trophys cause he was game sharing and Sony didn't help him at all. Good luck to u breh