Why does my Sims 3 (Origin) product Key not work?

I bought The Sims 3 off the Origin store. The transaction went beautifully. After installing it, I opened the launcher. I've played The Sims 3 before, but when my computer failed a year or two ago I lost the key, so I know most of what I'm doing, but I've never registered any of my EA games before, so I decided that this purchase I would.

I made an account and linked it successfully to my Origin account (I think, atleast that's what the website told me, and that's what it looks like). Then, I felt like going to download some custom content, so I get to the Exchange and discover I have to register the game first. Okay... that's fair, I suppose, only my product key doesn't work. Every time I put it in, copy+paste or manually, it says it's invalid. I can play the game with this product key perfectly fine with no problems, but I can't register it? So then I see if I click "What does this mean?" it says that if I bought the game off Origin (which I did) then it automatically registers it to my account.

LIAR. Straight up lie. It's not there, and what's more, is that it won't let me put it there. If it was there, then I could download addons but I can't. I can't even post on the forums to get help. Really? I bought the game and now I can't experience part of it because my product key which should be valid doesn't work? I bought the game today. Tried the key 1 hour after the purchase once it was installed. No one else uses this computer or has access to my accounts, and no one has stolen and registered my product key within that hour.

So, question is, why isn't this working, and how do I fix it?