Adding Expansion Pack to EA Account

I am trying to add the Sims 3 Seasons Expansion Pack to my EA account because my new laptop does not have a disc tray. I own the physical copy of the game but the serial code does not seem to work as it says it has already been used before. I don't understand how this can be, as I have never registered it with any other account, and I bought the game new back in 2012. 

I have been trying to use the Official EA Help Centre, but it has been connecting me to an "agent" for the last two hours... I am beginning to believe that there is no hope in sight.