IELTS letter ; Changing the booking of travel abroad

You have recently booked a trip abroad with a travel agency, however, plans have changed and you cannot go to that trip. Write a letter to your travel agent. In your letter

- Give details of your trip.
- Explain why you can't go on this trip.
- Tell the agency what you want to do about the booking.
Dear Sir/Madam.

I have booked a trip to Switzerland for me and my spouse, scheduled for September 15, 2013. I regret my inability to depart on scheduled date. Some inevitable urgency at my work insists me to put my personal plans on hold for a shorter time.

My PNR number on travel itinerary is 123-456-0134-4567. I would appreciate if you cancel all the reservations for this trip. I am really keen to experience and enjoy your elite trip. Since I am planning to make another reservation at earliest, I would appreciate if the amount I have previously paid will be used for my upcoming trip. If this adjustment is not possible kindly reimburse the paid amount to the credit card I have paid with. I am canceling this trip before 30 days of scheduled departure so as per terms and conditions I am eligible for the full reimbursement of the paid amount.

I humbly apologies for all the inconvenience this may have caused to you. If you have any questions, please feel free to call me on 123-456-7890. You can also approach me at jesse@gmail.com.

Yours truly,

Barack Obama

I think it is good if you introduced your booking in the introduction itself. Then they get a better idea about your booking;
This is with reference to my booking, ( give the booking reference) for the trip to London on the ???????? ?
Then express your inability to making it.
Kindly , have a meaningful topic in the subject field when you open a new thread so that you can earn more comments and feedbacks for your essays.

i think you should put your purpose of this letter on the first