When something is wrong with a product or service, a well-written complaint often resolves the situation satisfactorily. Use this format for a letter that gets results.
Prime the pump with a compliment. You bought the product or service about which you’re complaining, so there must be something good about it. Better results come with warmth than with wind.
If you’ve been a loyal or a high-volume purchaser, mention it. Even if this is your first experience with the company, it costs more for them to get new customers than to keep current ones. Their self-interest is served by a reasonable effort to make you happy.
Two or three paragraphs are enough. State the problem simply. Include specific information, such as the product code, date and place of purchase and sale-by date. Keep the letter focused on essential details.
Be specific about what would satisfactorily resolve the situation for you. From a free product or service to a refund, let the company know what you want. State your time frame for resolution.
Write a draft of your letter right away, while the details of the experience are vivid. Let the draft sit for a day, then edit it. If you flamed, tone it down. Check for grammar, spelling and clarity. There are many good sample letters on the Internet.