This letter is a follow-up to the first and second product complaint letters, and expresses your anger at having been ignored. This is the time to threaten further action.
1234, Main Street
Boston, MA 02123
<Recipient Address Goes Here>
<time you wrote the letter> I wrote you a letter requesting a reply to my first letter of <date of letter>. In both letters, I believe I made it very clear that I am very unhappy with my purchase of <product> and would like some action on your part to either refund my money or replace the product. To date, I have received no reply of any kind from <company name>.
Your complete indifference to the dissatisfaction of a customer makes my decision to conduct no further business with you an easy one. However, that does not free <company name> of its obligation to refund the purchase price of <product>, a poor-quality product which is useless to me. I expect this refund within <days to issue refund> days from the date of this letter. If I do not receive it, I will be taking my case and my story to <advocate or bureau>.
encl: <List of enclosed items goes here>