A Ridiculous Law

My son, who is 14 months old now,receives no means of support from his absent father. Brief story ..his father was physically, mentally, and emotionally abusive therefore, I along with my children left that relationship. When I went to the CSEA (Child Support Enforcement Agency) I was informed that ,there is a law,and because my son's father receives SSI, which is state funded , I cannot even file for support . The case worker stated " the state looks at it as if they( state) are paying the support for your child " . When she told me that, I thought to myself ...Ok , its crazy how he can purchase illegal material with that money and it is NOT traced but has a law that "protects" him from helping support , a child he helped create !! Its all just WAY BEYOND ME!! please help me understand !! Do u know the name of this law?