It's best to turn off Game Updates in Origin, before trying to disable any packs. Or else Origin will try to download the pack(s) you are trying to disable.
To Turn Off Origin and Game From Updating
1. Open Origin and click Origin in the menu in the upper left.
2. Select Application Settings.
3. Look for the Client Update section - Where it asks Automatically update Origin and/or the game, click Off.
When the option is off, it will be grey.
This will prevent Origin from automatically updating the Origin client and/or the game. it will prompt you to update when there is an update.
When it prompts you to update, you will need to log in with username and password and have the choice to update or play offline. Choose offline if you don't want to update Origin.
When in offline mode, you will not have access to the community gallery or other online features.
You can disable Vampires if you so choose, see link below for more details:
Disable Single Packs
http://sims4.crinrict.com/en/2017/03/disable-single-packs/