there’s always google chat or google classroom
or telegram as the last resort
the google platforms are tied to the students icon email too.
there are also mobile app (unlike SLS)
and those info on google chat or google classroom can also quickly converted or forwarded as email to prove to students that info has been sent black and white
again, you can mute notifications outside of working hours
or just not reply during your own well bring/self care time

all the above does not involve mobile numbers