The Knocking Sound

At three in the morning, I was woken up by a knocking sound. Knock, knock, knock. I looked through the peephole, but the hallway was empty. Just as I was about to go back to bed, my phone rang. It was a message from my mom, who lives next door. "Son, don't open the door. I just saw someone standing outside your door." I froze and immediately replied, "How did you know? Weren't you at your parents' house?" Mom replied instantly: "I am at my parents' house. But someone just called me, pretending to be you, and asked when I was coming home." At that moment, I heard my mom's voice from outside the door. "Son, open the door. It's Mom." My whole body trembled, and I couldn't make a sound. The next second, my phone vibrated again. Mom sent one last message: "Whatever you do, don't open the door... I just received news of your death." And the voice outside the door suddenly changed to mine. "Mom, he won't open the door. What should we do?"