The Watcher (2016)

A young couple's new home seems perfect. It has plenty of space to start a family and their neighbors are friendly and helpful. Then the couple starts hearing strange noises and they discover on their porch an envelope that has "OPEN ME" written on the front. The old, worn letter in the envelope tells them that some is watching them who believes that the house belongs to him instead of them. After their stalker starts sending gifts, including more notes, packages and damaged photographs, they call the police but learn to their horror that it might already be too late.