You can file a rule to show cause in your existing custody case. This essentially summons him to court to explain why he should not be held in contempt for failing to make payments as ordered.
Alternatively, you can call you local county prosecutors office and ask for the child support division. They may be able to enforce the existing support order through the Title IV-D court.
In either method, you may be able to get an income withholding order and have the payments come right out of his paycheck if he's employed.
This answer is for informational purposes only, and it not intended to create an attorney-client relationship. I've had only the limited amount of information provided in the question from which to form an answer. Your best course of action is to set up a formal consultation with a qualified attorney in your area.
I agree with my colleague Mr. Sokolowski, I only write to point out that many lawyers will ask you to make an appointment because they are busy and need to be able to set aside the time to meet with you at a specific time when s/he knows you are coming so they have your file ready to review with you. All of the things mentioned in Mr. Sokolowski's post should be done by your lawyer to avoid errors. If you are not happy with the way your lawyer is representing you you can fire him/her and find new counsel.
Best of luck!