Yoast plugin isn't working effectively

I have installed Yoast SEO plugin before one month in http://cloud-9-homes.com/. After this plugin i didn’t create any custom robot.txt and sitempap.xml because I came to know yoast itself create all these files but after 2 or 3 weeks still google webmaster couldn’t find out the sitemap and robot.txt. So i make both custom and uploaded. So please can anyone tell me how to make Yoast plugin effective without custom robot and sitemap.xml ? Thank you.