My ex was ordered to pay $50/week for our two daughters (he was making 60K/year as a PI). To relieve himself of that burden, he quit his job. At the time of our hearing, he owed my daughters 5K. The judge reduced that amount to zero as well because I was employed (in a minimum-wage job). He hired a great lawyer...I could not afford to hire one. The ruling stood, and I was given no recourse.
Although I must say, even after the years of poverty and struggle, I think my daughters and I have had the better end of the deal. He never bothered us again (he had threatened to kill all three of us over the measley $50/week), and hasn't seen his daughters in over 10 years.