Send him letters by certfied maill or by Fed-Ex or messenger to prove receipt. You may still not get the response you want (and maybe the lawyer has a legitimate reason for not responding, like if you're not contacting him for a valid reason), but at least you can prove receipt.
You can't report a lawyer who's not your lawyer to the State Bar. You can just contact him by provable method of delivery, and if he doesn't choose to engage you, he doesn't have to. He doesn't have to settle, if that's why you're calling. If you're calling to schedule something and he refuses to respond, schedule things when you want and refuse to compromise if he later complains. Many lawyers only communicate with their opposing counsel (and in your case, opposing party) when they absolutely have to, and prefer to create what they think is fear by not communicating extraneously and only using their litigation tools.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
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