First the easy answer. An owner is deemed to have received notice of the AGM if it was sent in time and it was sent to the address in the strata roll. That’s just the law and it applies to more areas than strata.
Warning to all owners, know when your AGM should be and follow up the secretary.strata manager if you don’t get a notice when you expect it.
Secondly. Did you submit your agenda items after the AGM was called? Items submitted after the General Meeting has been called can be discussed, but no motion can result from them, because they were not on the agenda.(The purpose of this is to ensure that owners who are not in attendance can have a vote on every motion)
Thirdly, anything resolved by a motion at a properly constituted General meeting, is what has been decided. If an owner was not aware of the meeting, the result of the motion still stands. If an owner gets cold feet and wants to change his vote, then the owner needs to submit a new motion ( to reverse the previous motion), submit it to the secretary/ strata manager and have it scheduled for the next general meeting.
The strata committee can also reverse the motion (at a properly constituted SC meeting), again if a motion is received from the aggrieved owner.
good luck