Violett, we've had this issue multiple times with several nicks... The only way we've found to fix this problem is for RoboOp to re-start the entire chat server, which is something that he really tries to avoid doing.
You may register another nick with no fee for the nickname change, very similar to your first one... VioletteFrances1 or something like that.
Then just keep trying on your other one. Usually it could be several months before Robo re-starts the server.
We apologize for the inconvenience this causes you. We honestly have no idea what causes this issue. Hopefully it'll be resolved soon.