Complaint: displeased with treatment

I am writing of a matter which I am confident will be of interest to you.

Since I know your firm to be one characterized by quality and service, I was quite surprised at my experience [DATE, ex. last Wednesday] with your [POSITION, ex. teller], [NAME, ex. Mr. Bill Williams]. [MENTION CIRCUMSTANCE OF BAD SERVICE, ex. Upon informing Mr. Williams that he had mistakenly processed a withdrawal instead of a deposit, as I had requested, he informed me in impolite and aggressive terms that it was "my problem." He then refused to process the correction.]

I will not trouble you with the details of the conversation, as it will serve no reasonable purpose. I am certain, however, that you will be concerned of the possible loss of business that may occur if customers are continued to be treated in this manner.

Since I know you wish to uphold the good reputation of your establishment, I trust this information will be of interest and use to you.

Sincerely,