I shared my Game Center details with my friend. He betrayed me and changed the primary email address of my Apple ID.
When I persuaded him a lot he gave back my Apple ID and Game Center and I quickly changed all my info. However I have found out that he still uses my Game Center.
I have another Game Center ID and I saw my own Game Center ID active 2 hours ago when I woke up in the morning. How can I log off the other device from my Game Center?