Child support collected by a state agency

[Desperate DAD]

I live in Arkansas and have a son age 16. I divorced his mother before he was 1 year old and "I" was awarded full custody of him in the divorce. His mother was on her way to her first of multiple times to be incarcerated and there was no child support stipulated in the divorce for her to have to pay.
When my son was around 11 years old he started having severe problems with behavior at school, at church and at home and I was strongly urged to have him tested (ie) evaluated and he has since been diagnosed with everything from ADD to Bi-Poler and he later got into trouble and I was asked by my parents to let them take custody of him to avoid him being confined in some kind of institution. I agreed and he went to live with them. A year or two passed and every time he would get into trouble my parents would have him checked into some sort of behavioral center to avoid him being sent to juvenile. Once my parents health got worse they asked me to let my oldest brother and his wife take over and the patern continued until he got into trouble in junior high school and him ending up in court could not be avoided.
He ended up in the care of Arkansas DHS, and has since been bounced around the entire state to finally now be housed at the state hospital.
I am barely able to keep track of him or his wellbeing because at the time he was taken into DHS custody he had been in the custody of my brother and his wife. My son draws SSI benifits because of the conditions that he has been diagnosed with , and I have been taken too court and forced to pay the state DHS child support in excess of $400 per month and slapped with a substantial arrearage because they waited quite some time before they notified me that I was going to have to pay them child support dated back to when his custody was transfered from my brother and his wife too DHS.

Please someone tell me if there is anything that can be done adout this?? My son also has Medicade which applies to his care and has as far as I know covered all of the facilities where he has been in the past.