IOS – How to disable the “Welcome, Name!” banner notification for Game Center

The simplest way is to delete the game from your iPad, which will destroy any local stored game data, and will prompt you to remove the app from Game Centre (which I assume you want to do if it's corrupt on the Server). Then redownload the app (or re-add it in iTunes in your computer). This should allow you to start with a clean slate.

Have you tried contacting your credit card provider?

Seriously, Apple's intention is that iOS Game Center friends are meant for "real" friends—rather than "Facebook friends"—so exposing your real name is not a threat. If you look at the issue this way, it feels more of a security enhancement than a threat. You can be sure the friend you are friending is actually the person you believe them to be.

Moreover, if you are underaged and can't attach your own credit card with your Apple ID, it is, in contrast, more secure to have the user's (kiddie's) name obfuscated.

Finally some legalese from the Game Center TOS:

The full name associated with your Apple ID will also be shared with those users to whom you send, or from whom you accept, a friend request, such as in the Friends list, the Friends leaderboards, and the pending friends requests lists; and we may recommend games that you have played to your friends. If you prefer not to share your full name or profile with friends, you should remove that friend by tapping the “Unfriend” button at the bottom of that friend’s screen in Game Center.

For each friend's account you need to force an update, you should unfriend them and then establish the friend relationship again.