I have the same problem
I registered my code for the beta and got the message that I should wait for the email for the psn code.
But until now no e-mail has arrived.
I have the answer!
First, you have to delete your linked console.
Next, log out and create a new Activision-Account (You need a other e-Mail for this).
Once you've created a new account, and link it with your Playstation, enter your Amazon code for the beta on www.callofduty.com/redeem
And your psn code appears.