Mom being contacted to Pay Child Support because I am working and dad's not.

I am a single mom with a 2 year old. I just got notice that my sons dad is seeking child support because I am working, and he inst, which he hasn't worked since our son was 1, and he is going on 3. We have Joint custody, but I provide for our son financially by myself with no help from him. I pay for his child care expenses, and he refuses to pay just the few dollars a week to help with that. He also applied for cash assistant, and because of this, it added another case for me to possibly pay child support. I make 12/hr and pay Rent, and my son's father stays with his grandparents. Is there a way that I don;t have to pay him or the state child support, I'm honestly pinching pennies with the responsibilities I have now.

Also his worker called me and told me because he is receiving aid from the state, I am considered the absent parent, even if this is not true.