It's not against the law to bypass geoblocking in the US either, and in both AU and US, you can (and probably have) executed contracts that prohibit you from doing that regardless of local statutes.
What proof would you expect them to need other than your login associated with requests to their website or their content CDNs from IPs associated with VPNs?
Its not a court of law, its terms of service. They can terminate your account without any recourse. That's how business work (unless you can prove they're discriminating against you based on a protected class).
