(In addition to @John's answer.)
Is there any way to tell Google not to index that site?
Rather curious that whilst they appear to have cloned everything (including your XML sitemaps*1), they have not cloned your robots.txt file. In fact, the robots.txt on that site actively blocks crawling of everything! So there would not seem to be anything to do in this respect. Doing a site search on that domain returns just the bare domain and a notice stating that its blocked by robots.txt.
(Rather curious what their intention would be in doing this? You could perhaps just assume that they made a mistake with robots.txt - and that maybe so - but this looks more like a deliberate exception to me?)
Also, whilst your XML sitemaps are cloned, they aren't updating the URLs in them (as they are doing on the main site pages), so they are still pointing back to your site.
*1 Regarding the XML sitemap(s). On your site "sitemap.xml" is actually a redirect to "sitemap_index.xml" and the cloned site has actually cloned the redirect... which redirects back to your site! (Surely a mistake on their part.) "sitemap_index.xml" is just an index, linking to 4 other sitemaps. If any of these actual sitemaps are requested directly on the cloned site then they are correctly cloned and the URLs updated. However, I would have said that these sitemaps are unlikely to be found on the cloned site because of the initial redirect of "sitemap.xml". (?) Although if they did submit "sitemap_index.xml" directly then that would obviously get around the redirect.