The only thing you can do is contact the person owning the copied site and let them know that their Indian developers have copied your sites. Playing the "sympathy card" might convince them to contact their Indian designers and express their disappointment. And the reason I mention that is because the Indian designers might have told them that their site is custom and unique (which would then be a lie). If clients start asking for money back because their site was copied, that might turn tables.
Just a thought.
If you need to prove it, try using the "wayback machine" to show them when your site was first put online.