My phone is just metal and plastic. It's new, but not working.

I bought this phone two weeks ago. It's fully charged, but the screen shut off while I called my friend. Her voicemail answered, so I tried to end the call, but I couldn't. I can't do anything really. I can't turn it on, off, restart... The call finally ended on it's own. I could hear it, but no visual.

Now it's just metal and plastic; a black screen.

This phone hasn't been dropped, soaked in liquid, nor have I downloaded anything, so what can I do?