4k tv not playing 4k

<p>So I bought a tv that was said to play 4k. I asked them to play 4k content on it they told me they didn't have the remote for the tv. There was another Sinotec next to it and that one was playing 4k content. I bought the 55" UHD digital LED one. I was told it would only play via usb i told them thats ok I would download 4k content. I have tried every single format and none of them are supported when it comes to 4k. I tried mp4,avi,mkv etc none of them are supported. It's strange because the none 4k videos play in that format. When I asked what format it was that the videos played no one could answer me. Can someone please tell me what format I can view?????????</p>