How can I get back the money I paid in child support, which the mother received by fraud?

She lied to the court and said the child lived with her, and he never did. He always lived with father because mother neglected him, and father provided all support. She lied and said that he lived with her, so got child support and welfare. That money was taken from me, and I think I should get it back. How do I go about getting an order for her to repay?