Hope my musings on the subject help. Letter writing is a lost art, especially when you want to get something from someone. A complaint letter should be sent to governments and politicians. All other should receive a letter - stating your disappointment with a wee touch of sadness lamenting that the product you thought so highly about, well.... let you (family/organization) down.
Providing the detail on model, lot number, and/or serial number gives reassurance that you actually have that product in your hand as you write.
Give then time to reply. But EXPECT a reply - if they don't - it tell you a lot about how they view their customers. Do send a follow-up letter referencing your earlier email of mm/dd/yy. The best follow-ups are actually mailed to the company via snail-mail.
Last thing - If they do resolve your problem. Send a thank you note. It helps pave the way for the rest of the folks behind you.
Let me know how it turns out.
Carl