Would definitely check the terms and conditions.
Maybe an argument around why it wasn’t practicable to cancel within the cooling off period? E.g. “Strewth mate, I was on walkabout and there was no signal in the creek”.
Dispute with the credit card company/bank perhaps?
Raise with the Aussie equivalent of the Ombudsman?
The UK Consumer Rights Act 2015 refers to things like the product/service not being fit for purpose or as advertised and you were mis-sold the product.
I’d also put on the socials what has happened and tag their customer service dept.
