It's one thing to accept the fact that your replacement bike will be delayed due to supply chain issues.
It's a different thing altogether to be given the silent treatment....and then just shrug your shoulders and say, "Oh well, that's life!"
Given what people lay out for bikes and how important they can be (for staying sane), I'd be pissed too if the manufacturer was incommunicado.
Letting the LBS know how displeased you are with Giant is just a first step. Then you should step it up with Giant; keep at it with (courteous and reasonable) emails to every customer service contact you can find, with CC's to the LBS. Keep at it until you hear something from Giant. If that still doesn't work, hit the forums, gather other crappy customer service stories and keep the topic on the internet radar. They have media people who's job it is to crawl the internet for what people are saying about their company; a few lines of code is all it takes for them to get automated emails every time somebody takes a dump on their good name. The more crappy stories there are, the more they make their way back to QC, and the more pressure there will be to reply in some form, issue a recall, a technical service bulletin, an apology, anything. And that's the key: being treated decently, getting heard, and receiving a reply.