If you would like to discontinue a service, it may be required that you submit a request to cancel your service in writing.
If the letter is being sent as a hard copy, then it should be in the proper business format, otherwise, if the letter is being emailed, it should have an appropriate subject line and proper grammar.
I currently have the Basic Maintenance Package with Landscaping Contractors; my account number is [Account Number]. I am writing to inform you that I'll be cancelling our contract effective on [Date]. Please refund the unused portion of the balance on my account and send me written confirmation that you have received this letter.
Thank you for your outstanding service over the past several years. If you have any questions, please don't hesitate to contact me at [Phone number]