Two things that it helps to know about copied content: If you can determine that the images and posts they are sharing are hosted on your site you may be able to handle the problem on your own. Visit their site and look at the source code to see whether the contents of your site are being shown from within a frame. If you can use tools to check the server headers while their site loads, you can clearly see where each resource (such as images) is loading from. If you suspect they are showing content hosted at your site and not theirs, check your access logs and verify whether there are images or files requested from another domain.
If you are certain that your content is shown from their domain and not yours, and you have tried to contact them either through their website or through their registration (which is getting to be more difficult) then you can contact their host. Look up their host using whois information. It can make a difference where (what country) their site is hosted at for that to work. Generally US and EU hosts will co-operate with claims of copyright abuse, but not all hosts in all countries co-operate.
Until you have a good idea of what they are doing, it may be difficult and time consuming to fight it. All over the internet people are sharing content that does not belong to them. If it was easier to make it stop, there might be less of that behavior happening. It takes time and effort to find out the details and deal with it.