Dragon Age Inquisition DLC not existing on xbox one?

Most common cause of this is being logged into the wrong account....by this I mean, you unlocked the stuff on Account A(main) and now are logged into account B and it doesn't show up.  If you are 100% sure you are in the same account, then I would suggest you contact Microsoft and talk to them.  If you happen to have the original codes or receipt for the transaction they can or should be able to track the game to the right account and verify that you own it, are on the right account and fix any issues therein. 

But if you asked me to bet a penny, I would bet you were logged into wrong account.

If only one account has ever existed on the Xbox, and Father, Mother, Brother, or Sister hasn't snuck into your game system to create an account on it, then like I said, I would contact Microsoft and discuss your account with them, and preferably have the codes from the game available or some form of receipt so they can track back and see what is happening on the game.  I don't think EA has anything to do with adding or removing things from Microsoft Xbox accounts, that should all be handled inhouse by Microsoft.