Hence the phrase
"with proper notice". It is not just that it is by text message. I suspect that additionally insufficient time was used. There is nothing legally wrong in itself with a landlord raising the rent, when it's done
with proper notice.
The requirement that proper notice be in writing is so that there is tangible evidence that notice was given, as the potential ambiguity or misunderstandings that can happen with oral communications. While text messages are not proper notice, they are at least more in the spirit of the definition than an oral communication.
I would be more concerned about the number of days notice of the impending rent increase was given, and whether the landlord abided by that.
This is Massachusetts, so perhaps
@Mass_Shyster will weigh in. Massachusetts, especially depending on where in Massachusetts, can be quirky.
https://www.masslegalhelp.org/housing/lt1-chapter-5-rent-increase