Dear (insert last name of contact here)
Paragraph 1: Bring the reader to the attention of your dispute immediately, and draw their attention to any attached documents which lend weight to your claim. This section should be between two and three sentences long.
Paragraph 2: Here you can go on to explain in more detail your dispute, and give invoice numbers or contract numbers that relate to the dispute so that they can find your case quickly and easily. Explain what is wrong with whatever it is you are claiming a dispute on, and go into specifics. Don’t leave any stone unturned and make sure you miss nothing out.
Paragraph 3: If you have anything that will help your case, such as a legal ruling which you know of, or a company willing to support you in your dispute then you should mention it here.
Paragraph 4: This is a concluding paragraph. Make sure you remain polite, but be firm about expecting a response in a matter of days. Lay out again your demands, and give a realistic time frame for resolution.