mass effect 2 deluxe edition.

I have bought the mass effect deluxe edition through steam quite a time ago and I enjoyed the game without the dlc for quite a while (I didn't realise I needed to activate it) so when I found out I didn't have the dlc yet I tried to activate it however my digital deluxe cerberus key seems to have been used allready.

Is there any way you can help me get to my dlc?

thanks for your time

Hanne