Screen Blacked out after phone was in back pocket

My phone was in my back pocket. i sat down on it i guess. i got it out my back pocket and it was cracked on the inside. The bottom half was completely black but top was i could see. but it had lines through it.it wouldn't even let me attempt my password meaning it wouldn't let me swipe on my phone. Sat it down and came back, the whole screen was black. What should i do?