I have found (as many can attest) that threating to s*** in their wheaties has worked for me.  Basically, I inform them that they have until X date to respond or I begin writing every person I can think of to damage their reputation, i.e. their parent company, the title insurance carrier they represent, the BBB, the attorney general in the state they are based in, the attorney general of any state they operate in, the insurance commissions in those states, etc.  You get the idea.  So far it has worked--no need for court action.  Now if they were out of business or in bankruptcy, none of the above would have worked because they wouldn't care about their rep.  If the client is an attorney, then the state bar.