I don't think The Sims 3 website keeps track of the CC you've downloaded from the exchange since they are free and re-downloadable, unlike purchased items. (If you uninstall the game, you may lose purchased items so therefore they keep track of your purchase history so you never lose the items you paid for.)
I guess you would have to re-download the CC you've lost. Use some of these websites other than the exchange for CC:
The Sims Resource: http://www.thesimsresource.com/
Liana Sims 3: http://www.lianasims3.net/
Spring4Sims: http://www.spring4sims.com/
My Sims 3 Blog: http://mysims3blog.blogspot.pt/
Simblr Download Directory: http://simblr-downloads.tumblr.com/
Anubis Under The Sun: http://anubis360.livejournal.com/
Orange-Sim Club: http://orange-sim.blogspot.pt/
Simply Kitsch: http://simplykitsch.tumblr.com/tagged/downloads
Shock & Shame: http://shockshame.tumblr.com/tagged/downloads
Next time, back up your CC by going to Documents>Electronic Arts>The Sims 3>Downloads.
Copy everything in the folder and paste it into a new folder. Save the folder somewhere where it will not be deleted.
I had to go through this as well, and I had over 100 CC. It was horrible. I'm sorry that this is the only solution. ):