Good evening, I will be appreciating to you if you tell me how to write official complaint letter to any company, it’s my first time writing this letter. I would like to know what is the propriety language to use.

Thank you for your help.

Moon
Complaint regarding what?
I don't think there is an "official" complaint form. I usually write a complaint email this way:

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Dear Company A,

- Introduce myself.

- Describe the probem.

- Tell them how you want the complaint to be resolved.

Sincerely, My Name

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I would be calm and factual. One usually gets better response that way.
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thanx alot