That is appalling. 4 months is way too long to wait for service.
Sounds like he does not have the business sense to recognize the fact that servicing a previous customer is at least as important as profits from new sales.
Personally, I would move on,,, what will you do if it requires service again? I’m in this hobby for enjoyment, not frustration.
We are lucky we have options...there are lots of wonderful phono stages out there. Buy yourself a new one and when this finally gets fixed and sent back to you, sell it. If there is lots of demand now because of a positive review, it should be easy to sell. If it were me, I’d have no qualms with posting the company name on this forum. Could help forum members contemplating a purchase. Might even speed up the repair if the company owner gets wind of the bad service review.