Did you ship $4-5K worth of anything without any payment? If a face-to-face has never happened, I'd be careful, even if a few years of online exchanges have taken place. It's definitely not the way I would like it to be, but the reality is that trust needs to be earned, not given too freely. It's also a matter of scale. If it's a low priced item, no biggie- I have done the same thing although, the last time I took the time to call a manufacturer and ship a car audio crossover, I never saw any kind of thanks, public or private.
I know how hard it is to meet a deadline when other things are happening and/or facilities aren't what I would really like. It was hard enough to admit it to myself that it wasn't going to happen but it can really hard to admit it to the person who's owed whatever it is. Nobody wants to say "I failed" but at some point, it's time to fish or cut bait.
Hopefully, this will be resolved to someone's satisfaction.