What playback devices have you tried with NOW movies , where i am assuming it's not live NOW TV movies that you are talking about and is on Demand movies which should be available ?
Watch this space for subtitles coming to live NOWTV in the near future.
If using a Youview box, then unfortunately NOW doesn't offer subtitles for this particular device.
Look and see if the Now app is available directly on your TV, and if not, maybe get an Amazon Firestick, at a Black Friday price.
These will definitely have subtitles on Now, where they are available.
Though note that an annoying and long-standing bug means that every time you start a new programme, you have to pause it, select the speech bubble icon that appears, and turn the subtitles on again.
Every bleezing time ?