I'm writing a complaint letter.

我在写一封抱怨信。

The mall gave no reply to our complaint letter.

商场对我们的投诉信没有给予回复。

I'm writing a complaint letter. It's about you.

我在写一封控诉信，是控诉你的。

The complaint letter should be firm but reasonably worded.

投诉信应该语气坚决并陈述合情合理。

According to the complaint letter, hotel maybe have the risk of lost customers.

根据投诉信，酒店也许有失去客户的风险。