Ignoring is in general the worst thing you can do, if they do anything more it looks bad on you in court.

I do agree with those who say get a lawyer to send your response. However you should still do the research yourself - to the best of your ability. You can save yourself some expensive lawyer time by knowing the basics and having a potential draft (be careful: make it clear that you do not have any emotional ties to it so the lawyer is free to tear it up) of your response.