For some people wagging the finger and giving a potch works, for others giving a hug works better.
Instead of forcing them not to text, yelling at them, telling their parents rabbis etc , give them a POSITIVE reason not to text, give them something else to do.
You catch more flies with Honey than vinegar
You want to make Shabbos a positive experience not a negative experience (ie A day of NO) You want them to look forward to Shabbos not dread it.