Update:
I received a text message from the Coles store manager last week, indicating he has a solution and would refund the unactivated cards. I was travelling (well, what else would an AFF member be doing) so went into the store on Saturday. Manager and assistant manager were not there, but the staff member at the service counter knew about my situation and provided a cash refund without hesitation.
I did not hear back from customer care department, but can only assume they worked with the store manager to arrange the refund.
Not sure I will be trusting Coles as a place to purchase Bunnings cards again. Would be nice if Woolworths sold Bunnings cards (now that Masters is dead, they may start to carry them as they do with Myer cards). That way I can purchase with discounted Wish cards.