Here is the famous Tower Rat DV sample letter.
TowerRat; What makes a good DV Letter
Another thing that gets neglected at times. Always understand what you are writing and sending in a dispute letter. A simple copy/paste of some of the form letters out on the net could have you end up in court. A C&D could be a disaster if not used properly. (Some have suggested it never be used, but I feel it has its usefullness if used properly.) Take a few days to research before you fire off that letter.