sims 3 bought from steam but ea app shows different product key

sanjayaloria1234​  The product code you're seeing is probably the one that the EA customer support rep added to your account in order to help with the underlying issue.  I don't think they could manually add the Steam product code to your account once it's shown as invalid.

That said, you can ignore this unless you happen to have an issue with Store content or anything else that might be related to the product codes.  In that case, you might need to switch to an EA App install.  So if you want to avoid that, are you within the refund window from Steam?  You could purchase the game again and try to register the new code to your account.

If your Steam and EA accounts are linked, however, the new code might not work either.  I can't prove this is the underlying issue, but there are many reports of Steam codes not working from players whose accounts are linked, as if the EA App detects the code and auto-consumes it before the player has the chance to register it on the Store site.  So if your accounts are linked and you don't want to unlink them, there's probably nothing you can do other than hope you don't see any negative consequences.