Did you purchase it from a retail store or did you buy it online? Either way, I imagine you paid on a credit/debit card? If thats the case you'll have proof of purchase I'd have thought you will be able to get it sorted.
Definitely not in an email or something?
If you still have it installed try Belarc Advisor,it can detect the product keys of all sorts of software including MS Office as long as they are installed.
http://www.belarc.com/free_download.html