Legal Question in Landlord & Tenant Law in California

You cannot countersue. The legal remedy for someone not served appropriately is to file with the court a motion to quash, and to mail a copy to the landlord's attorney. The documents should have a stamped case number on them, and should have a stamp that shows the date it was filed. The case would not appear in an online search because eviction (unlawful detainer or "UD") cases are masked so that the tenant is protected for up to 60 days.

Often, three-day notices are not handed to the tenant because they are not home when the process server knocks on the door. All the process server needs to do to serve a three-day notice is post a copy in a prominent place at the property and then mail a copy by first-class U.S. mail to the tenant(s) at the same address. I'm not sure what you mean that "it was posted on [your] door a month late." If the three-day notice was posted at least three days before the unlawful detainer lawsuit was filed and you did not pay the rent during that three-day period, then the complaint might be sufficient to move forward. If the lawsuit had been filed within that three-day period, then the landlord might have a problem.

Many courts have legal clinics either in the courthouse or nearby for people who can't afford or don't want to hire attorneys. You might check at the courthouse or online as to whether this service would be helpful.

Unlawful detainer cases are not searchable by the public for the first 60 days after filing. You need to go to court in person immediately with photo ID and find out from the clerk in person whether or not that case with that number is actually filed against you.