So, I was having this same issue on XBOX One. Although it is not stated anywhere, or not clearly stated where anyone can clearly see, this add-on only counts for a single EA account. Additionally, you need to be logged into EA to see the additional content.
Testing Steps:
1. Purchased on master account (mine), States "installed" on both master and child account (my son's account) -- or at least that is what you will conclude by reading the message on the child account. Add-on Content not available in either account.
2. Checked that all content was installed and there were not updates or downloads pending on either account.
3. Created an EA account to log in (I have avoided this so far to limit game play for my kids). Logged in on master account and the content was available, but even after reboot of the system it did not show up on child account.
4. Even though child account listed the content as "installed", I used the "purchase" option on the child account with a gift credit. Content still did not appear in child account game, but it now had a different "installed" message than it did before.
5. Created a new EA account for my son's child account. Verified the account in email and logged in. Content is now showing up on the child account as well.
Question: Where do I go now to get the add-on removed/refunded for my account. I never play these games. Also, who do we inform to put a message on the product to clearly indicate that it is for a single user account only!