My phone turns on but the screen is black

I have a galaxy J7. I was in the toilet on my phone listening to music i tried to change the song but my screen was black, it didn't fall, my screen has no cracks whatsoever. I bought my phone online (NEW) but maybe its refurbished and wasnt repaired properly. I've had my phone for almost a month and it never once fell. My phone can be turned on or off, you hear the little samsung sound when you turn it on, I can take screenshots but nothing comes up on the screen. Its just black. What can I do?