How do I get back the three dots user is texting on messinger

Hi!

Adding onto what HJA43 suggested, if iMessage is definitely turned on, try closing Messages and reopening it again: swipe up from the bottom of the screen and then on the Messages app.

If the three dots still don't appear, report the behaviour to Apple: Product Feedback - Apple.

Make sure iMessage us turned on: Settings-Messages-iMessage