@nicholsr Just another idea: First off, nobody is that busy that they can't spare a minute or two to float you a quick call and/or send you a quick text message providing some sort of information on the status of your repair.
Secondly, the idea of sending written communication via registered mail or the like is a very good idea. If push comes to shove, this documentation will seal the case in small claims court. However, if it is accurate that mail is not received at this person's shop, which I doubt, and you do not have his home address, then you could try this: You could contact the police in the jurisdiction of this guy's repair shop, explain your dilemma and ask if they would be so kind as to give you his home address. If, for some reason (e.g. confidentiality/privacy; etc.), the police wouldn't or couldn't share his home address with you, you could ask them or the police in the appropriate jurisdiction to do something called a "wellness check" to make sure this guy is OK. In the process, they would explain why they were there and why they were checking up on him. If need be (e.g. small claims litigation), this police report would be good documentation, as well.
P.S. Keep track of your expenses in trying to smoke this guy out. This would also be claimable in small claims. Good Luck!