Formal and Informal Letter Phrases

Dear Sir/Manager / Mrs xxx

Thank you for your letter that you sent …(week, month) ago/of the 11 May
In a letter you assured me that the….
It was pleased to hear that…
I am sorry to say but…
I am writing to complain about the…
I am waiting for a replacement
I am not satisfied with…
I will return for…
I have experienced a lot of problems with…
Firstly, your advertisement claimed that the…
Despite my initial disappointment…
I was extremely pleased to hear that…
I sincerely apologize for not being available…
You are quite welcome to (do something)……