By filing an answer or some other pleading in the case you have entered an appearance in the case and the improper service defense may not be available to you. That defense is best raised by an attorney before anything is filed in the case.
I provide a free 15 minute telephone consult for security deposit claims and eviction defense. No attorney-client relationship is created by answering questions in this public forum. If you wish to create an attorney-client relationship, you must contact me directly and sign a representation agreement. Answers are provided based on general ideas and an answer specific to your situation would require a review of all documents.
You needed to assert that defense of improper service before you filed an answer. By answering you waived your objection to improper service and subjected yourself to a jurisdiction of the court.
Please note that the above is not intended as legal advice, it is for educational purposes only. No attorney-client relationship is created or is or is intended to be created by my answer. You should contact an attorney in your area to discuss your case.
I agree with my colleagues that by filing an answer, you have submitted yourself to the jurisdiction of the court. If your answer raised defenses to the allegations alleged in the complaint, then I would recommend hiring an attorney to appear at any future hearings with you so he/she can properly argue those defenses and advise you throughout the remainder of the case. Good luck to you.
Please note that the above is not intended as legal advice, it is for educational purposes only. No attorney-client relationship is created or is intended to be created hereby. You should contact a local attorney to discuss and to obtain legal advice.