It's for You (S03E11)

For Christmas, Gary gets a phone line installed in his bedroom with the condition that he must not "misuse the privilege." Unsurprisingly, he starts making prank calls right away, but things take a turn when one of his victims begins to stalk him over the phone. When Gary decides to confront the caller, he finds himself face-to-face with Mrs. Emma Needham, a seemingly sweet elderly woman who quickly reveals that she's far from the pleasant persona she first presented.