Hamilton Beach Microwave Sets Fire company refuses to replace, Internet

I purchased a Hamilton Beach microwave approximately 4 months ago. It has been used maybe 6 times. Today I tried to bake a potato. The first was in for 3 minutes and 20 sec. The bottom of the potato was hard and crusty, the top was still raw. I chose another potato and placed it on a microwaveable paper plate with a bit of water to keep the bottom from becoming overcooked. After approximately 2 mu.irrational the plate caught fire. I called the company and even though it has a year warranty, they refuse to replace it because I didn't keep the box and receipt. I did mail in the warranty card but I was told that does not matter. Now I am out the money for a microwave that lasted only 4 months the representative stated I should have educated myself about their policies before buying their product. Then rudely began raising his voice when I questioned their methods and products.