Shitty as this behavior may be: Why would there have to be any payment? It's just an account with a private company.
They can setup arbitrary rules or ban you without any rules. It's their service, their database... Just like a club can throw you out on a whim. You may tell your friends and eventually that club may go out of business because of their shitty behavior but that's about it.
This would have been a whole other story if it had happened with the x.com domain name...