How can I remove these subdomains from google?
No subdomains have been created on my domain. But when I search Google by typing site:mysite.com, I see numerous subdomains and after 6-7 pages in Google I see my site link. How can I remove these subdomains from google?
Based on your screenshot, your hosting account is hacked or was hacked. Could still be indexed, but removed by host if they were aware of a server wide hack. If you can login to cPanel or DirectAdmin (or whatever) you will see if those subdomains exist. If so delete them. First take a screenshot and ask your web host how they got there.
Contact your hosting provider. Maybe you give someone access as an administrator.
If you are using WordPress, check. Or do a ftp search to remove
If you are using WordPress, check. Or do a ftp search to remove