Yes, child support is always one issue that can be reopened after a divorce (assuming there are still minor children involved). You could file you petition/motion for a review of the support issue in the New Jersey court on the grounds that you never received proper notice of the support action.
If the divorce court which awarded 50-50 shared custody still has jurisdiction over the issue of custody, the matter would need to be brought back up in that particular court.
However, if not and the child has been continuously in residence in New Jersey for at least 6 months or more, your petition for custody would need to
be filed and litigated in the appropriate court of that state.
