1234, Main Street
Boston, MA 02123
05 April, 2005
<Recipient Address Goes Here>
Please be advised that on <date(s) of complaint(s)>, I received <a complaint/complaints> about <nature of complaint(s)>. This letter is to place you on notice that this is a serious problem which needs to be addressed. Please immediately desist from further <description>. If, perhaps there has been some misunderstanding, I would appreciate you notifying me at once. Otherwise, I trust that I will receive no additional complaints in this regard in the future.
encl: <List of enclosed items goes here>