Don't Hang Up! (1974)

Amanda Post (Susan Bracken) returns to her childhood home to care for her ailing grandmother, Harriet (Rhea MacAdams), a place tainted by trauma from her mother's unsolved murder. As she confronts her past, she faces off against three unsettling figures: Doctor Crawther (Jim Harrell), who is suspiciously controlling; corrupt Judge Stemple (Gene Ross); and Claude Kearn (Larry O’Dwyer), a museum curator eyeing Harriet's valuable antiques. After dismissing their nefarious intentions, Amanda becomes the target of a threatening phone caller, who seems to know her every move and threatens her safety.