You file a demurrer like any other motion. A demurrer is essentially a motion challenging the adequacy of the complaint. You need a notice of demurrer, demurrer, and memorandum of points and authorities in support of demurrer. See my guide, "Essential Elements of a Motion in California" by clicking the following link: http://www.avvo.com/legal-guides/ugc/essential-elements-of-a-motion-in-california?ref=result_2_title
The demurrer will state that complaint fails to state a cause of action under Code of Civil Procedure section 430.10(e). (A claim which is barred by the SOL fails to state a cause of action.) By filing a demurrer, you need not file an Answer to the complaint at this time.
It is not clear whether the other side is contending that it has effected a personal service or substitued service. If latter, the serving party normally delivers a copy of summons and complaint to another person and mails additional copies to you. A substituted service is deemed complete on the 10th day after mailing so that a defendant served in this manner has 40m days after mailing to respond. If you are not certain when the service was effective, I would err on the side of caution and respond by the earliest plausible deadline.
If you think the service was defective, another possible response is a motion to quash. Good luck.
This response is for information purpose only and does not constitute a legal advice. This response does not create an attorney-client relationship.
A Demurrer relies on the CCP code, sections 430.30, 430.40, 430.50, etc., and is filed and calendared and served the same way any other motion is made. Demurrers run the unique risk, however, of educating the other side as to any defects, and they may just amend their complaint to allege that your oral contract was within 2 years of the date they filed their complaint.
No, substitute service is 10 days from the date of mailing, no matter how long it took whoever accepted service to actually reach you.
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