Cherry,
The reason for my question was just to make sure you didnt expect the company to take action against the person who treated you badly.
While I agree, if it was my company, I would take adverse action against a customer service individual who treated someone in that manner, I think that the most you can expect in that regard is for them to use it as a training conversation..
I think it will make you feel better to let this company know of your experience.. That is why I recomend you send the letter..
and who knows, you may get a new discount coupon...
Good luck