"I am not a number, I am a free man."
Well despite the Prisoner's protestations, I'm afraid he is and he isn't. A number can be more individualistic than a name, because any number of people can have the same name, unless it is a rather unusual name. And besides the Prisoner didn't mind having the number ZM73 for identification during the course of the kind of work he did. It was not until the Prisoner was abducted did he make his protest. Possibly his protestations had more to do with having his identity taken away from him, and becoming just a number. After all the Prisoner does think a great deal of himself, of being better than anyone else in the Village. Not being subject to the rules which govern society within the Village.
As for being a "free man," he's no longer that, not since his abduction to the Village. But then perhaps the Prisoner is referring to the fact that he had resigned his job, that he is a "free man" to do and go where he pleases.
Be seeing you