When a customer is dissatisfied with goods or services, a complaint letter will inform the company or organization of the problem. Such a letter should both present the facts and express the customer's dissatisfaction.
Because a complaint, unlike a claim, does not necessarily call for action or compensation from the company, it should be answered gracefully. Indeed, the writer of a complaint is offering help to the offending organization, an opportunity to improve its operations. Therefore, the response to a complaint should be concerned and courteous, not defensive. It may offer an explanation and suggest remedies that are being followed. It definitely should extend an apology.