Online pass issue, but not a new purchase

@BlackDaLina

If you like, you can try the flowing troubleshooting steps in the meantime.

First, try to clean your Origin cache:
 
    - close Origin completely. (right click on the Origin symbol in the task bar > close)
    - Press the Windows key and "R" at the same time.
    - Type or copy  "%ProgramData%/Origin" (without quotes) > hit ENTER
    - Delete all the files and folders in the Origin folder, except for the "LocalContent" folder. (The "LocalContent" folder must remain untouched.)
    - Press the Windows key and "R" at the same time.
    - Type or copy "%AppData%" (without quotes)  > hit ENTER
    - Now your Windows explorer should have brought you to your "C:\Users\>your user name<\AppData\Roaming" folder
    - Delate the "Origin"  folder inside the "Roaming" folder
    - In the address bar of your Windows explorer click on the word "AppData".
    - Open the "Local" folder
    - Delate the "Origin"  folder inside the  "Local" folder
    - Restart your PC. > test

If that not helps, and If you only want to play the Single player DLCs as you said, put this tow DLLs into your ">drive<:\Program Files (x86)\Origin Games\Mass Effect 3\Binaries\Win32" folder.

This DLLs are made for the purpose that the DLC check for games with mods get approved.  EA or Bioware don't have a problem with this DLLs as long you use them in single player and with a registered copy of course.

I however don't know if this DLLs will work in regards to your problem.