You don't.
Read Carefully: [url]http://www.bungie.net/en/View/bungie/eula[/url]
You are LICENSING the rights to play Destiny.
Any content that may have been on the Disc at time of purchase is not yours it belongs to Bungie and Activision.
Therefore you were never cheated out of any content as it was not yours.
If this is unacceptable to you there was a 30 day refund policy granted to you in the terms & conditions that you probably didn't read. If it has been more than 30 days you have no one to blame but yourself.
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Bungie stated back during the open beta that the content for the first (FIRST DLC was going to be released on the retail disc to make it easier for customers of the game whom had CRAP internet connections to be able to download the patches and play the DLC faster. if people would pay attention and stay informed, they wouldnt be immature crybabies now.