Yesterday I purchased the Blackwood Collector's Edition Upgrade from the Eso store on the website.
Everything worked fine: correct transaction and confirmation mail received. In the billing history of my account I can see the purchase too.
In game I can't find the bonus mount for the pre-order, plus I can't see that I own the new chapter and I could still be able to buy it.
I'm in the EU megaserver (but I play also on NA) and from PC.
I submitted a ticket (210530-007842) and replied it because I didn't solve the issue, still waiting for an answer.