Ghosted on Warranty

I had a mechanic rebuild the engine in my car. He operates from his personal shop and advertises on Craigslist. He warranties his work with a 12 month/12,000 mile warranty. I am now having issues directly related to his installation and notified him, asked him to return my call, and have sent several text messages detailing what I have found and what I think the issue is. He has not picked up or responded. He was very responsive up until I paid the $3000 for his service. I first contacted him about the issue three days ago. What can I do?

Location: New Mexico USA