Are you using an HDMI connection between whatever you're using to get NetFlix and the TV?
If so, that would explain your problem: audio is sent over HDMI over the same wires as the video, but during the "vertical retrace interval". That is exactly the same way Closed Captioning is sent. In other words, Closed Captioning and HDMI are not compatible with one another. To see Closed Captioning from an external device, you must use a "composite video" or "component video" connection.
However, if you have a "smart TV" and it is getting Netflix over the internet, then the problems is more likely to be in the TV settings, since HDMI is not involved. For help with that, you'll have to provide the exact model of TV that is being used.
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