Should I file parental kidnapping if my ex is trying to avoid me and my time from my son?

I am a father of a 9 year old son. First she moved into Maryland from New Jersey without my consent. Now recently she moved from Maryland back to New Jersey. We both have joint custody however she has residential. She moved into Philadelphia for a few weeks to a month before moving to New Jersey. I found out she moved from Maryland to Philadelphia, I asked her and she denied it and asked me to call the school if I didn't believe her. I did and they said my son does not attend the Maryland school. She said her phone doesn't get good reception, and the phone screen broke so she can’t make calls however I call her constantly and she doesn't pick up. What should I do? I love my son dearly he is my only child and I’m 37. He repeatedly says he wants to stay with me. He even cries when he has to go back to his mother.