It's great to hear you got your machine back! I'm sorry you had to go through this. It is not rude of you to enquire about what is going on with it, especially since you bought it from them. It is VERY rude of them not to return your calls and to leave you "out of the loop" of what is going on, or make vague excuses instead of being straightforward.
I've worked customer service too, and the key (as someone said) is communication!
Regarding Janome, I bought my machine on ebay, but I can email them and they will help me with my questions. I don't think, in this case, Janome is the issue, it is the dealer.
Since you have warranty it might be worth the 2 hr. drive to go to a reputable dealer if something happens again.
btw, was it the motherboard? My machine died and I took it to a small town guy and he replaced a fuse. He also let me take a video with my phone so I would know where it is and how to change it myself the next time. He wasn't even a Janome dealer.