They know you are overpaid. They are requesting information from you because they want to contact you and start the discussion process with you. This is their standard operating procedure. They have the records of your fraud. They really don't need a lot of information from you. Believe me, they've heard every sort of sad story and self justification you can possibly imagine. They're just giving you a chance to begin the dialogue. They'll have you a decision soon enough. Then you start trying to pay it back. If you do not, they up the ante, start garnishing wages, start collecting tax refunds, and eventually if they want to, they can recommend you for prosecution.