The Texas Attorney General has suspended my drivers license and has now filed a lien against me for back child support

My son is 28 yrs. old and never lived with the mother, I had no contact with my son from the time he was app. 4 yrs. old until he was a teen, then not again until app. 6 yrs. ago. My current wife started a business with her inheritance and we were able to purchase a home in 2008, I was paying consecutive pmt.s and had been to a hearing with Att. Gen. who wanted to drop the debt then but ex spouse refused, however the 2009 depression, if you will, and the gulf coast explosion cut our income immensly, we are oilfield inspections, and we have lost or sold most of our assets to survive and pay my current wifes high medical bills and now my ex wants to push the 29 year old debt because she thinks I am rich. What field of attorney do I need to seek and what should I base my case on?