Nigellas I went to school in an area that sounds fairly similar to yours- lots of kids bussed in from outlying villages, and this was before you could assume everyone had a reliable internet connection (obviously you can't assume it today, but it was a time when lots of people didn't have internet at home). Mobile signal was, and still is patchy too, and there were some people who didn't have landlines. My school did seem very careful with things like detention, suspensions, school trips, activities etc, that they would never put anyone (even sixth formers) in a situation where they could end up stranded.
I sort of think people who don't live in areas like this don't really appreciate that it does bring extra difficulties, and in an ideal world, schools would be extra careful with making sure that communication is sorted, as it's not as easy as things can be in other areas. Sometimes, these things don't seem like minor details either.
I don't think it would be unreasonable to say you understand the school fulfilled their statutory obligations, but communication is difficult for you right now- and it would be good if they tried a back up method as well- e.g. leaving a message on your phone, sending a letter home with your daughter, anything else they can suggest. Hopefully, the school is used to dealing with things like this and will be sympathetic, and try to do this if the situation ever arises in the future.