'This is a violation of the Strata Property Act and your Strata Corporation's Bylaws ... bylaws.' I don't get the weird capitalisation nor the concept that someone can be in 'violation' of their anything. Then, 'If we do not hear from you ... ' I see... But is the problem that they think they have some guy outnumbered or that he's a really bad shot?
Regardless if a "notice" is legitimate or not, a response is required... even if one's response states, "Screw off." - stay in honor and respond back, as much as it is a pain in the ass and you may be dealing with a bunch of thugs.
The bylaws likely say the fine is valid unless the council accepts otherwise, so you can't rebut the obligation... You agreed to the bylaws by joining the strata.
AFAIK A 'strata' is one of those body corporate / multiple occupancy type schemes that are frequently abused by shonky fucks to give theft and misappropriation the appearance of legitimacy.