I'm clearly in the wrong here, but hopefully it's a lesson that will help others be vigilant in their dealing with LinkedIn Australia.
Surely a receipt or an invoice is the bare minimum they should do. Awfully scummy of them.
It's not a convenience question. Either they throw it away for you, or they put it in the bag and you throw it out yourself. Maybe even with the bag.
Then I realized, it could only be because they hope for you to agree to making the item no longer returnable. No receipt, no return. So you (potentially) only shoot yourself in the foot by saying no.
As you can see, LinkedIn have optimised the forgotten trial cancellation to a fine art.