If you have joint established custody and one parent moves the child to an undisclosed location without notice to you and refuses to let you communica

What state do you reside in? I need the state to be able to tell you the laws on a custodial parent relocating with out the consent from you, or the court. In most states the father can file and get custody of the child if the custodial parent relocates without the consent of the non-custodial parent or court. There is a statue of limitaton on the non-custodial parent to file for custody after the custodial parent mves, again it depends on your state.

It's probably a violation of the child custody agreement.

If you are wanting to file charges against your ex for parental kidnapping then you would need to get in touch with the law enforcement authorities and request they assist in the return of your child. Parental Kidnapping Prevention Act states that if a party (such as yur ex-spouce) refuses to return your child, you may seek relief under the parental kidnapping prevention Act (PKPA), Contact the local enforcement authorities and request they assist in the return of the child. If they refuse, INSIST that they enforce the PKPA Statue. Local law enforcement is bound by law to enforce the PKPA, and it is NOT up to them to selectively enforce it OR to decide the merits of any specific case or situration where the PKPA is applicable.