my sims 3 account is saying that I have installed seasons but it isn't letting my install the Origin Exclusive Trick-or-Treat Costume Pack. I tried to register my game again and it said invalid code. I went to the website http://www.thesims3.com/incentive/ep8origin and it said to enter the unique code you received from Origin, which I am assuming is the serial number it gives me, and that is saying invalid code too!!
You should have gotten a second email with the code for the trick-or-treating costumes.
If you didn't, contact Customer Support
They can be found here: https://help.ea.com/contact-us
Choose a category, a game and a platform for the option so show up.
If live chat is gray, change your country to US and make sure you're on US Business hours. It might also gray because they're very busy. Try later.
See this post if you have trouble with the site: http://sims3.crinrict.com/en/2012/10/how-to-contact-ea.html
