You say that other people "found out from family members and friends". Who has been helping you with the application process so far?
If you've been doing it without help from a parent or someone more knowledgeable than yourself, then that can't have been very easy. Unfortunately, that makes you responsible for doing the necessary research. If you've been receiving guidance from a parent etc., then it was their responsibility to make themselves (and then you) aware of this deadline - as with all the other deadlines associated with applying to university.
However, I agree that it would have been useful if your school had mentioned it too.