They will show on your Flying Club account, the Premium upgrade one appears on your account a few days after your anniversary date and the Companion one appears as soon as you hit the spend threshold.
My companion voucher appeared the other day:
31st March 2018 02 April 2018 VAA Credit Card Companion Flight Qualification 0 0
Worth noting that if you are viewing your account via the desktop version, you do need to click on the ‘Activity’ tab to see these as for some reason these vouchers don’t show up in the ‘My account activity’ list of transactions you see on the main page after logging in!