two servings in a bag, I was tricked

It was 11:00 pm and Alicia sat in the school hallway. Her phone was almost dead and all the offices were closed. She sat waiting for the call "I'm here" from her sister, Valentina, who was on her way to pick her up.
"It's so cold here," she said after a while and walked to the vents on the wall that pushed warm air into the hallway. She sat down with her back in front of one of the vents and ate fruit snacks from the vending machine in one of the lower floors. She felt tired, so she lowered her head on her lap. Ten seconds passed when she heard a voice behind her, "Alicia, I'm down the hallway."
Alicia lifted her head quickly and turned around. The vent was behind her. She said nothing. Then the  voice said again, "Alicia, I'm down the hallway."
Alicia jumped to her feet and slowly turned her head to the right.

"Who's there?" she asked hesitantly. There was no reply. Then warm air from the vent swept across her face and with the air came a voice again, "Alicia, I'm down the hallway."
"Valentina is that you?" Alicia asked. Her sister must be playing a joke on her. There was silence.
In this moment, Valentina pulled up in front of the school as she dialed Alicia.
Alicia spoke again, "Valentina, stop playing games with me."
After she spoke, her phone began to ring. The air from the vent turned cold. Alicia was too scared to answer the phone. Her body was frozen in place. Why would Valentina be calling her on her phone if she was down the hallway? The phone stopped ringing.
As Valentina dialed again from the car, Alicia found it difficult to move. A black figure appeared at the end of the hallway. Her phone rang again and went directly to voicemail.
"Ali, I'm outside. Hurry up. Hurry up, Ali. It's freezing out here."