Improper service of the summons and complaint often is your primary weapon to seek relief against a judgment. Here's a blog post discussing the basic law involved in that process.
Establishing lack of personal jurisdiction due to improper service should be enough to get you a hearing on that issue. But I implore you to first get a copy of the affidavit of service and dispute every fact you can in your affidavit when starting the process. To get the affidavit of service, you can order it from the court or ask the collection law firm for it. Judges need to see you rebut the facts of service with specificity. Conclusory denials that you did not receive the papers is not enough.
If you do dispute the affidavit of service with sufficient detail, it should be enough to get you a hearing as to service ("traverse hearing"). Collection lawyers will argue that you must also provide an "excuse" for not appearing in court and a "meritorious defense" to the underlying case. But
Advisory Notice 13 confirms that a good showing of lack of personal jurisdiction (i.e. bad service) avoids the need to provide an excuse and a meritorious defense. Bring this
notice to court.
Of course, it is always best to also provide excuses and meritorious defense in addition to facts establishing bad service. The more robust your affidavit, the better. Civil court judges will be pleased with the effort you put in to protect yourself.
Of course, contact us right away if you want an attorney to protect you, which is often the best route to take.