From the Cubic Castles Terms of Service:
4.You will not submit content that is copyrighted or subject to third party proprietary rights, including privacy, publicity, trade secret, etc., unless you are the owner of such rights or have the appropriate permission from their rightful owner to specifically submit such content;
I know that many children don't understand this so I will explain it for you. I have seen characters in game named after tv, movie, anime and book characters. You need to know that those names are actually the property of the people who created them. Here's an example.
J.K. Rowling created the name Harry Potter. She owns it and is entitled to be paid real world money any time anyone uses that name. Therefore, in game you cannot use the name Harry Potter or any kind of version of it such as HaRry Potter, Harry Pott3r, or any other name that includes Harry Potter unless you have written permission from JK Rowling. This means that you can not use the name even if your own real name is Harry Potter. I know that seems unfair, but that is copyright law.
The problem with using copyrighted names is this: no one is going to sue a seven year old, but they may (quite rightly) sue Cosmic Cow for lots of money which would result in losing a very nice game.
Here is my suggestion if you are using a copyrighted name. Contact CC support and explain that you did not realize that you didn't know that your character name was not useable, and ask them to allow you to change it.
Copyright law is a real law, not just a Cubic Castles rule. It applies to all the games you play where you create a character name for yourself.
Hoping you do the correct thing,