Lost registration code

Do you still have the game installed on a computer ? If not, contact Customer Support. If you can prove that you bought the game, they should be able to give you a new one.

Here are the instructions on how to get the keys from your registry (PC only). Credits fo to Carl's Sims 3 Guide

You need to be signed in as an Adminstrator first.  Windows may require your permission to open the
Registry Editor and if so, just click on yes.

1.   Press the Windows key on your keyboard and type regedit in the search bar and press Enter.  
2.   Click on 'File' at the top left of the window that opens then click on Export.
3.   Choose a location and name for the file as this will be your backup registry file.
4.   Click Save.
5.   This backup is created just as a precaution.

Now to find your serial codes for each specific EP or SP installed on your computer:

1. Expand the HKEY_LOCAL_MACHINE folder.
2. Expand the SOFTWARE folder (Wow6432Node for 64 bit systems)
3. Expand the Electronic Arts folder.
4. Expand the Sims folder
5. Expand the EP or SP you need the code for
6. Click on ergc and in the box to the right under 'Data' you will see the code
7. Write it down somewhere save
8. Repeat above steps for each EP

Have you lost the disc, or the whole game?

If you've lost the disc, you can login to your Origin/EA/TS3 account by downloading Origin (http://origin.com), and then you can redeem your game code and download it from Origin.

Try contacting EA Customer Support via. the phone, it's toll free - if you're not in the states you could call it via. Skype.

They are a lot more helpful than the web team. If you still have a receipt, you should be fine - if not try calling and see what they say. 

+18665435435

I have the same problem, but it would help if somebody in the Sims 3 department would actually answer my call. Very displeased right now.