We hired him in a talent website, when I say he disappeared is because he was just unavailable to continue doing the voice over for us, he was not available for booking anymore. I suspect this company reached out to him, booked him heavily or something so he was not available for us.

My guess is that their voiceover guy had an exclusivity agreement with the other company.

He could live in a jurisdiction that enforces non-compete agreements, or he could have been currently employed by the competitor with a full-employment clause in it.