2 difference game center acc created with the same email address?? what happen to my old game center acc?

I got my first game center ID with the nickname "thewinnn" with using ipad 2.

After few months, i tried to use my iphone4s to login to game center with the same apple ID/email, but i failed to retreived my game center ID with "thewinnn"!!! and the system asking me to create a new nickname !!!

Can someone tell me what happen and how i going to retrieved back my old game center ID with the nickname of "thewinnn". Thanks