Dear Mr. ,
I would like to inform you that we are cancelling the (service or purchase to be cancelled) effective one month from receipt of this letter. I am sorry that we have to cancel our (order or service) with you for the reason that (specify reason for cancelling order or service). I have been a customer of yours for quite a while now and I have been satisfied with your services in the past. I hope that my cancellation will not cause any problem with your company. I am willing to pay the amount specified in your company policy regarding cancellation of services.
Please send me a written letter to confirm the cancellation within the week. If you have any inquiries, you may contact me at the address stated above.
(Your Name and Your Signature)