They won't take the money off you. If your Ex has overpaid you, they will reduce the amount he has to pay you until the debt is paid. So, say he pays you $60 per month but somewhere along the way he has overpaid you by $100, they may make it that he pays you $50 per month for 10 months to reclaim his $100. Make sense? Because my Ex estimates his income due to working for himself, sometimes I get a debt to him that means I get reduced payments from him, other times he has a debt to me which means he pays me more. I have never had to give money back.