Thank you for your prompt reply. They haven't applied VAT specifically.
The invoices just states "Includes Tax" on a separate line which calculates at 20%
After some more digging, I have found...
Canva as an Australian company
Keep your country of registration updated to ensure you are paid and taxed correctly.
As an Australian company, Canva withholds royalty tax according to Australian law. The percentage of this tax is based on your country of residence. It differs from country to country, and is affected by any bilateral tax agreement with your country. See Income Tax Treaties for the list.
In many cases, any tax you’ve paid this way can be claimed as a foreign tax credit when filing your own tax return. So we advise checking your local requirements on foreign tax claims.
Australian tax year
After the end of each Australian tax year (1 June - July 30), Canva sends a Withholding Tax Statement, which summarises your gross earnings and tax withheld.
You may be able to claim credits for taxes withheld from your country’s tax authorities. We advise speaking to a tax professional in your country of residence regarding this. Countries without tax treaties may not recognise tax withholdings.
So I'm guessing, that I process as per above - no vat to be reclaimed - then once per year, I'll process a VAT refund claim based on their annual summary. I'm beginning to think the hassle is not worth the subscription!