Hi DAVETHEPHOTO,
I understand that you need assistance with associationg the VAT number during paying for Office 365 subscription. Please contact Customer Support for assistance with your requests, this article provides detailed steps for your reference, please click here.
You can also contact our Toll-free phone support in your region here.
I also noticed that you have concern about pay for the domain name at Melbourne IT. Based on the situation, you can contact Melbourne support for assistance. Please see buy a domain name. After that, it needn’t pay for the domain name anymore on Office 365 side. You will work with your own domain names in Office 365 service by adding and verifying your domain.
Thanks,
Maggie Li