Already Dead (2007) on Netflix

Plot summary

An attack leaves Thomas Archer's wife hurt and his son dead, with no motive he can see. A distorted voice on his mobile phone sends him down to an underground room, where a man sits tied to a chair with his head covered. The voice tells him that this man carried out the attack. Archer has no proof of his own, yet he accepts what the voice says. Implements lie in the room, and he begins to use them on the man while the voice gives orders.