It will be done in arbitrage before anything like that. It is perfectly ok to sue a business for inappropriate actions that are not clearly stated or wrongfully done. After closely reviewing Github's policy and terms of service. They do not state they will change your username(with or without notice). Unless the account is "inactively held for future use." I highly doubt OP had been inactive enough to be considered a squatter. Either way, Github needs to update their policies describing why and how someone like OP had to have their username changed without notice. If this happened to me with a username that I carefully crafted and was unjustifiably acted on. I would certainly speak with support then sue them if there is no resolution, hoping to settle out of court because going through the court process is a giant pain for both parties.