Good to know that Rakuten's customer service is willing to help out. I haven't used them much lately, but at least back then when they were EB****, I got my discounts pretty reliably and had a handful of issues resolved easily by customer service.
UCS AT-AT is tagged with "Hard to find" but shows up when you view the Exclusives category. I used PC (redirect from Rakuten's site, didn't use their extension), made sure to disable my ad blocker, and added to cart after the redirect. Really happy to get this set with a good discount.