译文 我写这封信是为了投诉……
点睛 本句型是典型的投诉信件的开头。complain about sth.是固定搭配，表示“抱怨某事物”，about不能替换为其他介词。
句型拓展
I am writing to express my dissatisfaction with your service. 我写这封信是想表达我对于你们服务的不满。
I beg to call your attention to the fact that your service is very dissatisfactory. 我想请你们注意，你们的服务非常令人不满。
I wish to refer you to an incident which occurred last Friday, calling for some remedial action. 我想告诉你，上周五发生的事急需采取补救措施。
I very much regret to have to inform you your service is very dissatisfactory. 很抱歉地告诉你，你们的服务非常令人不满。
I am totally disappointed to find that your service is very dissatisfactory. 你们的服务非常令人不满，对此我很失望。