Your letter is very good, short, clear and factual. I really like it, but do you have a specific reason to not mention that they refuse to let you know which elements convinced them that you are a multi-account abuser (except being lucky enough to manage to earn few dollars before getting limited)?
By the way, could you tell us which browser and which email provider you are using? Do you think someone(playing at Stake too) could have been able to access your emailbox from his own computer?