Legal Question in Civil Litigation in California

If the default was not entered before the response and cross complaint were filed, your default judgment will not be entered and you have to respond as if the filing was on time (technically you could move to strike the response and X-Complaint, but even if it was allowed they would be granted leave to appy to file it late and that would be granted). If the default was entered, however, even if the default judgment was not yet entered, then you still have to respond, but a motion to strike the response and x-complaint would be well taken. They still eventually will probably have leave to file late, but you can ask for fees and expenses of the default and motion to strike, and they will have to file a motion for relief from the default before they can file.

Bottom line is it's all a matter of how much trouble you want to go to to yank their chain. Since eventually they will be allowed to file, you could just deal with it as if it was timely and the case will go forward.