Heather, thanks for making that point! As someone who worked many years in retail, I was always much more happy to help the people who were sweet and nice than the ones who were nasty and rude. I think in general, this is a good rule to live by! I know this is a bit OT, but I'm glad it was brought up.
Hopefully the OP will be able to get her invoice or something and Uppa will make it right. Luckily lots of people here brainstorming can help out!
Also, for those buying products, lately, if I don't buy a big product online, but rather in a B&M store, I've been scanning my receipt into the computer so if/when I lose it, I still have some record of the purchase. Not sure if that will be enough, but at least it gives the date/time/store/purchase price...