Trouble with converting trail to full purchase |elements 9|

I had purcashed Photoshop elements 9 a few years ago, back when all the computers had a disk drive. My new computer doesnt have a this feature (like most) but I know you can redeem your past purchases via serial code. In my photshop account I have the serial number registred and recognized as a product but when I go to enter the same numbers on the 'liscence this software' window, it has an error message saying that the serial nurmber is invalid. I know this is an authentic adobe purchase because I bought it from Best Buy (plus it has that shiny reflective 'genuine' sticker on it) I lost the redeption code slip so that's a bust. Is there any way to redeem my elements 9 software? I don't have the money to buy a new version or sign up to a membership. I really like adobe and I need a specific tool on it to finalize an end of the year project for college (due tuesday!) 

Please help

-thank you