Manufacturers with Excellent customer service

Well, I sent a Moscode amp to George Kaye to get a upgrade on the amp
 and I have NEVER RECEIVED my amp back from him, then when I would call him all I got was it is not ready and the runaround. Mr Kaye
if you are reading this I would like my AMP back!! I know it has been a 
few years. Please Be the upstanding Person I think you are and do the right thing !!!!

That’s outright theft

i would contact the DA’s office in the county where Kaye is located 

Though not relevant anymore, the best customer service I’ve ever experienced, and I mean in any industry not just audio, was with Thiel Audio. Though everyone, and I do mean everyone there, was great, I have to give special mention to Shari Graham.

A small claims suit is also a good idea. Years back I bought a refrigerator but weeks passed without delivery. I demanded a refund. Radio silence from the store though I had been in contact several times a week to resolve this. Finally started a small claims case. When they were served the store called and asked me what this was all about. I told the guy- come one- don’t play games. Got a judgment which was served. 
I received a full refund plus court costs