I just found out one of my page was copied by someone and using it in their site, will google ban us if they found out this? Any advise. Thanks
You can file the papers for copyright infringement (DMCA Note), which is provided by Google. Google won't ban you. If you complain then they will get banned.
Google will take which ever content was indexed first into consideration more. You can also file a complaint as mentioned above.
You first step would be to content the webmaster and try to either get the content removed or attempt to obtain a backlink or reference of the original content. Then, if that doesn't work try contacting the hosting company and let them know a user of their service is illegally posting your content on their web servers to be displayed on that users website. Third, you can try a DMCA, but Google is slow to null on replying to these for content that is not legally copyrighted by a patent or book. http://www.google.com/dmca.html