Writing a complaint letter requires you to be clear and concise about the problem you are facing and the action you expect from the recipient of the letter. Here is a general format that you can follow:

1. Heading: Include your name, address, and contact information at the top of the letter.
2. Date: Include the date on which you are writing the letter.
3. Recipient’s information: Write the name, position, and address of the person or organization you are addressing the letter to.
4. Salutation: Begin the letter with a formal greeting such as “Dear Mr./Ms./Dr./Prof. [Last Name].”
5. Introduction: State the reason for writing the letter, including the details of the problem you are facing. Be specific and avoid being emotional or angry.
6. Body: In the body of the letter, provide supporting evidence or documentation to back up your claim. Explain the impact of the problem and the action you expect from the recipient to resolve the issue.
7. Closing: In the closing paragraph, summarize the problem and reiterate the desired outcome. Also, thank the recipient for their attention and consideration.
8. Signature: Sign the letter with your full name.
9. Enclosures: If there are any supporting documents, mention them in the letter and attach them as enclosures.

Remember to keep the tone of the letter professional and avoid using offensive or abusive language.