Unexpected increase in plan charges

Seaside Girl, Hello.
Judging from the amount, it seems that the contract was for AUD 39.99 at the campaign price.
As pointed out by John T Smith, the campaign price applies only for the first year. The price will shift to the regular price after the second year, so it is probably because of that.

If you have an Education subscription, the terms you "click to agree" should be clear about the first/later years
-One Year Intro Price https://community.adobe.com/t5/Get-Started/Student-plan/td-p/10209357

The regular plan also sometimes has a lower introductory price for the first year

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