You should send a letter to the attorney listed on the pleading you received asking for verification of the debt. Most importantly you should not let a default judgment enter against you. This means that you must file an answer within the time stated in the court papers you received. It appears that you are saying that you have the defense of simply not owing what you are being sued for. You may also have other defenses, and a possible claim under the Fair Debt Collection Practices Act against the entity suing you.
To determine your possible defenses and possible claim you should consult a consumer attorney in New Jersey, many of whom give free consultations. You should do this promptly so that if you and they determine that they should represent you in court, they have time to file an answer.
Madeline is absolutely correct. Call a consumer attorney right away. Make sure you or your attorney files an answer. Under some circumstances the other side will have to pay your lawyer. Don't wait for them to respond to you to file something in court.