Sims 3 pets DLC on xbox 360 not working after purchase

There are two things you can try:

1) Clear the cache memory of your Xbox 360 

2) If the 1st steps doesn't help, please uninstall your game, redownload it from Xbox Marketplace and install it again. 

How to clear the cache memory: 

Power on the Xbox 360 console. 
Navigate to “My Xbox”. 
Select “System Settings”. 
Select “Memory”, highlight the storage device, and press “Y” on the controller. (Do not press the “A” button.) 
If there are multiple storage devices on the console, it doesn’t matter which storage device is selected as the cache is cleared for all storage devices. 
Select “Clear System Cache”.

Please let us know if that helped!

Thanks,

Ursula