If the parent who is ordered to pay child support does not pay, the custodial parent can can file a complaint for contempt against that parent at the Probate and Family Court where the order was made. See  Complaint for Contempt (CJD 103) pdf format of Complaint for Contempt (CJD 103)
file size 1MB and Instructions pdf format of Ins for Complaint for Contempt

After you file a complaint for contempt, you will receive a contempt summons with a hearing date for a hearing on the complaint you filed.  See Service of Process for instructions.  DOR will file the complaint and serve it if you are receiving TAFDC or if you make a written request for their services. At the contempt hearing, the judge will review what the current order for child support is, listen to what the parties say, and consider the information on the parties’ financial statements. The judge then decides whether the defendant parent has failed to obey the court order and is in contempt, how much is owed and how it will be paid. In certain circumstances, the judge has the authority to sentence the Defendant to jail. 

DOR can also collect overdue child support without going to court. These are called administrative remedies and include taking the non-custodial parent’s federal and state income tax refunds or driver’s license. See DOR's child support page for more information.  

Most Probate and Family Court Departments have active “Lawyer of the Day” programs in which attorneys volunteer to provide free basic legal advice. Call the Registry of Probate of the County where you live for specific details.