Alex - under Australian consumer law- you can demand a refund and they must comply. There is no need to get jiggy wid them.
https://www.accc.gov.au/consumers/co...s-and-services
specifically:
Products must also:
match descriptions made by the salesperson, on packaging and labels, and in promotions or advertising.
match any demonstration model or sample you asked for
be fit for the purpose the business told you it would be fit for and for any purpose that you made known to the business before purchasing..
In other words - if the salesperson said it was USB3 and it is not - they must refund the money.
I'd ring them up and ask nicely...
and have the ACCC website ready to quote from.
Having said that - i would find it strange if a modern lappie does not have at least one USB3 port - especially one costing a Gorilla.
What model of lappie is it?