what is teletext (subtitles or close captions?) USA names
we are USA, are you? wiki says its UK DEAL .
tried here long ago and DIED. (no demand)
you posted to computers for a TV why do that?
what is the content of your viewing,
local broadcast direct
Cable
or streaming video.,
each have there one rules.
I'd bet what ever is the content does not support Teletext.
or only this movie or content NOW.
read last section cessation here.
https://en.wikipedia.org/wiki/Teletext
dead as of 2013, 7 years ago? but no country stated in your post making all answers , impossible, really.
nor content watched/.