This is a unfortunately the reality of buying online merchandise. One has to check the T&C and change of mind refund policies prior to purchase, and always check the web sites for their real national origins (not the perceived one) including physical contact information not just web forms or emails.
Since they did refund you 20% they may have written off their profit. I note Pain Relief Australia is a SA company and has phone and address information posted.
Consider this topic about clothing
Other than pressing the issue of acceptable quality it may best be written off as an ‘educational expense’.
If you press the quality issue you will need to collect evidence it was sold as a high quality product and considering it marketing claims and price it was not a quality product as represented, probably a long shot but nothing ventured nothing gained.
A final comment
What one ‘hopes for’ (assumes) and what one ‘explicitly asks for and then is sold a product that does it’ are quite different under the ACL regarding rights.
