Definitely don't purchase it a 3rd time. If I understand it correctly, they don't offer refunds on store content.
You may want to try to contact EA Customer Service to see if they can check your account to see if there's anything that can be done about it.
Though I have read about this happening in the recent past with other players. Give me a little bit and I'll see what I can find via search.
Edited to Add:
My Google-Fu seems to be a little off today or something. I couldn't find anything really recent, like I thought I read about.
Anyway. A couple of troubleshooting tips came to mind:
1. With the Sims 3 launcher open and logged into your store account, go to the DV page directly from a different browser to see if you have the download button?
https://store.thesims3.com/dragonvalley.html?categoryId=126422. Check to see if DV is in your Downloads Dashboard?
https://www.carls-sims-4-guide.com/forum/index.php?topic=16094.msg307126#msg307126 -- I have had luck with both these tips when I've had issues downloading store items.