This letter is regarding the [complaint/claim/letter] you [sent/submitted] on [some date]. Before even attempting to explain the reasons leading to this unintended mistake, I would like to sincerely apologize to you for any inconvenience this may have caused.
At [company name], customer satisfaction is something that we take very seriously and would never compromise under any circumstances. Unfortunately, sometimes unavoidable mistakes happen. In such rare cases, a satisfactory solution is always in place and preventable measures are introduced.
After a thorough review of your case, I have managed to pinpoint the reasons leading to this error. [Explain in two or three sentences why the error happened. Don’t make it long. The client is not really interested in the reasons, only in the resolution. But you should explain for the sake of completeness]. This is clearly a mistake from our side and we take full responsibility for it.
In our attempt to serve you better and retain you as one of our valuable customers, we are going to [state your resolution to the mistake: refund your money, give another item for free, provide you with one year subscription, etc…]. I hope you find these actions satisfactory and up to your expectations. This is the least that we can do to address the unintentional inconveniences that we caused.
As an extra measure to our unconditional commitment to customer satisfaction, we decided to [state measures and precautions that your company will take to prevent such errors in the future]. These precautions will ensure that such errors will not happen again in the future. This would not have been possible without you drawing our attention to your case. We take this opportunity to thank you for your feedback which allows us to serve you and other customers better.
We value your business and hope to retain you as a customer for many years to come.
Please always share your feedback with us; this is how we keep learning and improving. I am very confident that the next [letter / email] we receive from you will be that of appreciation.
Best Regards