Link …sitemap.xml opens website with blog content

Hi, I’ve installed the latest version and when I click on the link for the sitemap (https://www.fdp-voelklingen.de/sitemap.xml)it opens my blog instead of the sitemap. Also Google webmaster tools recognizes the sitemap as html file and gives me an error. I’ve also deactivated all other plugins but I don’t know what causes this error.

https://www.ads-software.com/plugins/google-sitemap-generator/