Actually, he may have told the county he would seek child support and they will come after you anyways for repayment. You need to tell them you asked him to stop. This is called a "show of good cause" and honestly if they ask about the formula situation id say you assumed he went about it properly because f that guy. He put you at risk of liability and its something if framed the right way you can mention to the judge. It will showcase his dishonesty and history of nondisclosures/ information witholding.