Since they are your former employer, I would call them out by making them give you an exact accounting regarding why you were overpaid and the amount. Send them a return letter requesting the details. Under Florida law, the employer can have a claim for reimbursement if they have overpaid, but as a practical matter they may just let it go. Depending on the amount, I would send the letter and wait to see how good their reason is and how serious they are about pursuing it. If it is a larger amount, you should probably visit with an employment lawyer or business lawyer in your area. If it is a small amount, it would simply be a small claims action they would have a right to pursue, at which point you could resolve it (sometimes w/ payments).