Robots.txt was genereting automatically

How old is your site? Check your privacy settings. Did you allow search engines index your site or not?

Google is not indexing my webpages

Did you check your webmaster tools account? If not how did you come to the above conclusion?

yr ago i have strted this website.
in my webmasters account it displayed “Sitemap contains urls which are blocked by robots.txt.”

so i got a doubt and opened the robots.txt directly and found that code. i havent created any robots.txt and its not there in my folder too

Look for robots.txt file in your site’s root. You can just delete it and replace it with a robot text file allowing search engines access. Even if there is no such file, SEs will index your site.

physically its not there in the root. but if i try to access it directly https://www.mysitename.com/sitemap.xml
its showing this code :

User-agent: *
Disallow: /wp-admin/
Disallow: /wp-includes/

Sitemap: https://www.mysitename.com/sitemap.xml

Try creating a robots text file as in this link and upload to your root:
https://codex.www.ads-software.com/Search_Engine_Optimization_for_WordPress

modified. tnq hope it will be solved