My Game Center Nickname Changed on Its Own

Like the title says: my game center name changed on its own. A few hours before, my name was Kirika_Pixel, then, out of nowhere, it was changed to something else. I tried to change it back, but it said my name was taken. I tried to see if this was true by sending my old name a friend request. No reply. I run IOS9 on an iPhone 4.

Please help me. I lost all my game data and I don't want to restart from level 1 😟