This is the 5356th most frequent Russian word.
отмене
"Отмене" is the dative case form of "отмена," meaning "cancellation."
The word "отменой" here is the instrumental case of "отмена" and denotes the reason for the cancellation related to the concert.
В связи с отменой концерта были возвращены билеты.
Due to the cancellation of the concert, the tickets were returned.
The word "отмена" is used as a noun subject, referring to the act of canceling something, in this case, classes.
Отмена уроков сегодня произошла из-за погоды.
The cancellation of classes today happened because of the weather.
The word "отмены" is used in the genitive case of "отмена" to express the possession or possibility related to the concept of cancellation.