There should be contact information in the letter received. This would be your best bet, since it’s the likeliest way to get through to the office that sent you the letter.
You can also find the New Jersey Division of Taxation’s contact information at NJ Division of Taxation - Contact Us.
They’re bound to be extremely busy this time of year, as you suggest. If you still have trouble getting through by phone, you might try emailing using the information in the link above. That way, at least you’ll have a record of trying to remedy the situation.
