Your choices are very limited.
You can hire an attorney, assuming this is not a small claims court action, but that will cost you a good amount of the total in controversy.
You can move to change venue to a forum more convenient for you, but unless the majority of the evidence and witnesses are in the other venue, it is likely not going to be a successful move.
You can negotiate a settlement because the costs of carrying on the lawsuit will quickly make defending it unreasonable.
You can stop defending the case and a default will be eventually taken against you and the plaintiff will have a judgment to enforce against you.
Or, you can continue to do what you have been doing.
There are really no other viable alternatives. Good luck to you.
This answer should not be construed to create any attorney-client relationship. Such a relationship can be formed only through the mutual execution of an attorney-client agreement. The answer given is based on the extremely limited facts provided and the proper course of action might change significantly with the introduction of other facts. All who read this answer should not rely on the answer to govern their conduct. Please seek the advice of competent counsel after disclosing all facts to that attorney. This answer is intended for California residents only. The answering party is only licensed to practice in the State of California.