Sims 3 Monte Vista Serial error???

Go to MY PAGE then scroll down to MY ACCOUNT then to REDEEM A CODE then REDEEM A CODE once more then enter the code. This works for Monte Vista and Hidden Springs.

I found it on my own once the customer support guy made me mad.

Hope it works for you as well.

ik heb ongeveer hetzelfde probleem alleen zeggen ze bij mij dat de code al in gebruik is weet iemand hier een antwoord op? 

I have recently purchased Monte Vista and it is coming up with:

The code you entered has already been used. Please check the code entered and try again. If you continue to receive this error it may be that the code has already been applied

Yes, I have confirmed that the correct code is being used- I have just taking the plastic protection covering of the game. How is this the case???

NOT HAPPY

Where did you try to redeem the code ? On thesims3.com where it says redeem a code or on Origin ?

Try to redeem the code here: https://store.thesims3.com/myAccount.html