I am very angry at EA merchandise consumer respect!

so you bought a used game and are upset you had to buy a key to play online, this isn't something new, a lot of companies have done this.  The fault here lies with gamestop for not telling you, in the UK game stores tell you it cannot be played onlne without an unused key.

as for buying a used key from the psn store, I suggest you contact an EA game advisor.  there isn't anyone here who can help with this matter, they are the only ones who can look into it for you.