Unfortunately, I am obliged to cancel our appointment.
I am sorry to inform you that our meeting will have to be postponed.
We regret to inform you that due to circumstances beyond our control, it is impossible for us to arrive in New York on time.
I hope you will understand that it is impossible for me to meet you in Oslo.
May I suggest that we postpone our appointment until later the same day?
I will attempt to arrange a new meeting at the earliest opportunity.
We will refund your expenses and contact you shortly to arrange another meeting.
I must apologise to you for this unfortunate turn of events.
Please accept my sincere(st) apologies for the inconvenience (caused).