J.H.
I went through this same situation about 16 years ago. Initially my ex was ordered by the judge to pay a minimum of $139 per month + 1/2 of child care expenses. At the time he was only making minimum wage because he was trying to get the lowest amount possible to pay child support. The first 2 1/2 years of my child's life I didn't see any money. I went to the office of recovery services, they started garnishing his wages for the $139. I have had the same situation when he did not return my son on time, I called the police and reported to recovery services.
Now to change child support agreement it is difficult, but you can do it and ask for a review every three years. They will base the new child support amount on what he makes, any custody issues you should also address at this time. Keep in mind this can take several months to complete this processes and sometimes over a year if your ex fights it. I would not let my son see him if he refuses to give you his contact information. I would go through recovery services because they can collect child support for you, and by law he has to give them his contact information. I would address all of the concerns you have with them or an attorney. If he is disagreeable in anyway, you need to seek legal advice immediately before anything goes any farther. Good luck.