Simply replace the unfilled areas such as "" and "[date]" with your information.
A business providing a service is only as good as the work done for its last customer. I am writing you this letter because of my extreme dissatisfaction with your services that were provided to me on [date].
The issues concerning me with the services I received from your company are as following:
1) [1st complaint]
2) [2nd complaint]
3) [3rd complaint]
At this point I'm not sure if I will ever use your services again. I'll leave the ball in your court.
If you wish to contact me my phone number is [phone #] and my e-mail address is [e-mail address].