Out of State Visition Violation

I live in California and my ex lives in North Carolina. We have 3 children together that I have been raising almost on my own. He owns me over 67K in back support. Yes I have a court order, but what good is it. Last year I lost my job and I let one of our children go live with him, with an written agreement that I will get him during the summer and any school break. Now it is summer and he is refusing to let my son come visit me. The order was part of a marital settlement agreement filed in the courts when we divorced in 2006. Now that he is out of state, I have not been able to collect support, but now he is keeping my son from me. What can I do?

Is your agreement filed in CA or NC?