I'm having a similar issue with the JNCDA course. Finished the course and pre-assessment two weeks ago but still haven't received a voucher. Truth be told, I had to put it on hold for a while to finish JNCIP-SEC but I don't see any mention of a time limit anywhere.
to get jncda exam voucher then u need to pass the assemeent exam test 65q. If your exam pass then it will automatically popur said your pass and it will send voucher straight to your email. If not then it means you still fail.
As I mentioned in my post, I did all of that but did not receive the mail. Anyway, I sent a mail to the Genius team yesterday and I promptly received the voucher code. Exam booked for tomorrow evening :-)