In junior high or elementary school we watched a film dramatisation of Ray Bradbury’s story Dial Double Zero. A guy answers his phone and says, ‘Hello?’ IIRC, there was at first no answer so he hung up. The phone rings again and he says, ‘Hello?’ A mechanical-sounding voice on the other end says, ‘Hel-lo.’ He keeps receiving these calls over and over. I think the voice eventually sounded human. I don’t recall how it ended.
From what I could see last night, the story was never published. I have not been able to find the film online. It does not appear in a search on IMDb. There is a film about the writing of the story. I have not watched it, but scanning it quickly I didn’t see anything I remembered. I’ll have to watch it to see if it’s actually the film I saw decades ago.