I would see what an attorney says, or the SS office, or you might just have to call the Child Support Enforcement office in your district. You could call your local Department of Human Services, or what ever those Texan's call it...LOL Okie here. There is an 800 number in Oklahoma but we also have a local office that they don't have a phone number for. You may have to do some searching to actually find out where the office is and go as a walk-in.
In my opinion there isn't much they can do to him for non payment except try and keep the tax refund, there is very little garnishment on disability. Maybe $25 - $50 a month. If he is remarried or files with someone they can file injured spouse and get their part in full refunded to them.
I would think any of those offices would be able to give you accurate information but until a Judge has decreed a change to the child support document then all the child support is due.
I appreciate your situation, really I do.