Here are some suggestions for writing a complaint.
– Explain the problem in the first sentences.
– Remember that you are unhappy with the company, not the reader.
– Keep the tone professional, not informal. Do not use a lot of emotional words (e.g., terrible, the worst…)
– You may to include a positive sentence about the company or your previous experiences with the product.
– Be specific about what action you are requesting.
– If this is a very serious complaint, explain what additional action you will take if the company does not take care of the problem.