Alright so four days ago I bought The Sims 3 Plus Pets at Best Buy. I couldn't install The Sims 3 because everytime I entered the serial # it said it was invalid. I tried calling tech. Support but was on hold for an hour an a half so I gave up. I went back to best buy the next day and told them the problem and they could exchange it for another game with a different serial number and I could try that but I wouldn't be allowed to return it again if the serial number doesn't work. So I got The Sims 3 installed, but when I try to install the expansion pack, Pets, the serial code is not valid..again. I am not sure what I should do? Send it back to the company since it has a 90 day warrenty?