I've been trying to buy it for a few hours, but every time I go to click on it it brings me to an expanse package instead.
That is strange... is this happening in the website or the Origin client?
Try to use this link to get to the purchase page, are you able to buy it there?
Check out our Sims forums for tutorials and all things Sims.
Try these steps first to clear up any problems you may have when connecting to an EA game.