Quantenmechanik-2 said

I create a User name with letters, number and a Symbol, but the system don't take it. Why?

Hello Quantenmechanik-2,

Well, it can't be the username you use for this support site (that is accepted). It can't be for a Firefox account either, as your email address would also be your username.

So, it has to be for some other account/website ...... Usually you would get a message saying that that username is already being used, or the characters/symbols you use are not acceptable.

You should contact the website ......

Do you really mean the user name or do you mean the password?

Requirements you posted above are more likely meant for a password. A user name usually doesn't accept symbols (only letters and number and a dash and underscore are allowed).