Received via email. I've got 2 cards and both of them received the same email.
Some good deals -
Credit will be applied to your Club Plus account upon activation and is available for use until 11.59pm Sunday 28th August 2016. Credit can be redeemed at any Supercheap Auto store or online at www.supercheapauto.com.au. Club Plus Terms & Conditions apply. See website for details.
Mod: Only existing Club Plus members who have the marketing checkbox ticked in my profile will receive the credit, if you have that ticked you should have received a $5 credit email (contact SCA if you have not), otherwise tick it now for next time.