Enigma for the Devil (1975)

Original title: Enigma para Demônios

After the death of her father in Argentina, Elza returns to Brazil to see her remaining family. When visiting her mother's grave, she steals a flower off an unknown grave and put it in her mother's. After that, she begins to receive strange phone calls, from an unknown voice that claims: "Give back my flower!". She becomes terrified and obsessed with the stranger's voice, and starts believing that it's the spirit of the deceased.