Do you have a sitemap setup in the content tree using the Google Sitemap XML webpart? Also do you have the site settings configured with this URL? Settings>URLs & SEO>Search engine optimization>Google sitemap UR and Google sitemap path. They should have settings similar to what I have here:
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The sitemap path is where the sitemap resides in your content tree. The sitemap URL is what you provide to google. For instance, www.yourdomain.com/googlesitemap.xml