7th Floor (2013) on Netflix

Plot summary

Sebastián is a lawyer in Buenos Aires with a major case on his hands. He and Delia are divorced, and their children, Luca and Luna, live with her in a seventh-floor apartment of an old building. Delia intends to relocate to Spain, where her father lives, and asks for sole custody; Sebastián will not agree. One morning he comes to collect the children for school. Delia goes off, the two of them race down the stairs on foot while he rides the elevator, and when he reaches the lobby neither child is there. The janitor and a neighbor, Rosales, a police detective, help him comb the building. Delia hurries back. Then a woman telephones, naming a ransom of a hundred thousand dollars and giving him two hours to produce it.