Subject
Complaint about [product or service] on [date]
Opening
I am writing about [brief description]. On [date], I [purchased, booked or contacted] [product or service]. The issue is [clear factual summary].
What happened
I expected [reasonable expectation], but [what occurred]. I have already tried [steps taken]. This affected me by [brief practical impact].
Resolution
I would like [specific remedy]. Please respond by [reasonable date]. I can provide receipts or supporting records through a private channel.