Before running to a lawyer he should at least send a paper letter. Skip this email and phone BS.
Certified, Return Receipt, signature required. Even a lack of response is still documented. Right now it's just he said/she said. And if it does get to the legal level, having an official and actionable paper trail is a lot stronger than "they haven't answered one email in 9 years". A judge isn't going to care about that (right or wrong is irrelevant - email is not as actionable of communications in business vs. mailed correspondence.)
If they still don't respond to a letter like that and it bounces back from the post office then you really have something for an attorney to start with. Attorneys are expensive - do the basics first before engaging one (if you have to).
And no, engaging an attorney does not automatically = a lawsuit. Quite the opposite, actually.
That works for many things. Many years ago Microsoft acquired a phone company that we had apps in the app store for. We had documented proof of the sales receipts but no payment. After months of nothing, I printed and sent an invoice by certified mail with signature requested and we were paid shortly thereafter.
If they still don't respond to a letter like that and it bounces back from the post office then you really have something for an attorney to start with. Attorneys are expensive - do the basics first before engaging one (if you have to).
And no, engaging an attorney does not automatically = a lawsuit. Quite the opposite, actually.