Are you based in Australia?
There is no way they can pay tax to the Australian Government without an ABN. It also says on their website that they don’t pay taxes on the merchants behalf… I’d be checking this too.
In order to check whether you’ve been paid for shipping revenue, you’d need to provide the proof. I’ve provided the proof and I still can get a resolution! Note, I’ve only had issues with the Shopify payment gateway, PayPal has paid correctly.