Respected Sir/Madam,
With all due respect, I would like to state that I am _______ (name), working as a _________ (designation) at _________ (organization name).
Through this email, I would like to update you regarding the _________ (name of the event) that was going to be held on ______ (date). I would like to inform you that the management has decided to cancel the event due to _____________ (mention reason for cancellation).
Therefore, I sincerely apologize to you for the inconvenience caused to you. If you wish to contact us regarding this matter, you can always reach us at ___________ (contact details).
Regards,
___________ (Name),
___________ (Contact details)