Speaking from personal experience, the last time they did this, I purchased directly from my credit card, and I never got the voucher code in my email (and yes, I checked my spam folder). I read the fine print and it said it had to be from the wallet. I was pretty pissed.
Maybe I got unlucky, but the next time I go for this promo, I'll add to my wallet first.
Did you check your message inbox on your console? Apparently sometimes people don't get an email but instead get the code through the message system. There was a person on a different thread accusing Sony of purposefully deceiving its customers and whining about everything when it clearly said it could be sent through the console message system.