I bought the Mass Effect trilogy used, and while both ME 1 & 3 have given me no problems with accessing/purchasing DLCs, ME 2 is out for blood.
I’ve tried to purchase the Cerberus Network from the main menu, but it says that premium content is not available for my XBOX Live account and I’ve made sure all my privacy settings allow for that content. I’ve tried to purchase from the marketplace in the dashboard and from the marketplace at the Microsoft website. Neither worked. All the forums that I’ve read (which are a lot) had solutions only work for PC. My region is the US/North America so I believe that’s not the problem.