@teewee55 If Dragon Valley shows up in your purchase history, that means the code you were emailed was already tied to your account. Finding it wouldn't help, as codes can't be registered a second time. It's strange, though, that the store isn't letting you download the world. Have you tried both downloading directly from Purchase History and from DV's main page? (There's a tab on the left labeled "worlds," which will list every world and link to its page.)
If that doesn't work, try clearing your browser caches, including the one for Internet Explorer. Even if you never use it, the store does for some purposes. Be sure to uncheck the box to preserve data for favorites. You could also try a different browser. I've never had an issue downloading through Firefox.
clear IE cache: https://kb.wisc.edu/page.php?id=15141
If none of this helps, you'll probably need to contact EA customer support and have someone on that end look at your account. Perhaps something needs to be reset. Since you still have access to the email address with which you bought DV, it shouldn't be that difficult for support to confirm your purchase and issue you a new code, if necessary. But it might help if you could provide a screenshot of your store purchase history showing you own DV.
https://help.ea.com/en/contact-us/