Your best bets are to go to Sony Customer Support with the code and see if there's anything at their end they can do to rearm the code. If there's nothing they can do then the next port of call is Activision.
Getting a response from Activision is like getting blood from a stone, so unless customer support can help you, your voucher codes are about as useful as toilet roll.
Sorry. 
You can contact Customer Support through the numbers on the other side of this link, and the Activision support website can be found here. If you choose to talk to Sony, or Activision, being polite, patient (despite the problem) and concise can get you a long way 
Just trying to get the post some attention... i've logged in but there's no where to post comment
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