Help on changing back my iPhone Internet carrier?

So about a month or two ago I changed my carrier logo to the abstergo symbol and it showed me how to change it back but it won't work. It says "no matches found" when I try to change it back to AT&T. And I need to change it back because there's a problem with my phone and I don't want them to see it.

If you JailBroke your iPhone to do that there's no way to change it back. Once you change the logo of you phone from AT&T it's gone for ever