Sorry to hear of your problems, but unfortunately it's not the first issue we've heard with that model.

Seems there are still a few teething problems at the moment.
With regards to the strap, the exchange was probably just for the watch head (as that was the part with the issue) not the strap as well. The replacement watch head was probably supplied to the AD without a strap, so while it would've been nice to get a full brand new watch, the replacement was probably for the head only.
Certainly not good though if the AD managed to scratch the new watch by mounting the strap! That's a fundamental mistake to make, and one that you should quite rightly go back to them about.