For anyone else having this issue I finally resolved it myself. The free trial form doesn't use the email address in you Azure account info/profile or the Visual Studio developer profile. It's using the details in the Billing section of the Azure portal. Steps below to resolve:
- Log in to the Azure Portal
- Go to the Cost Management and Billing section
- Open the 'Settings' subsection
- Click 'Properties' - the email address / telephone number displayed here are the ones that the Azure free trial form is populated by.
- Click the 'Update Sold To' link
- Update your contact details to the correct values and Save
- Navigate back to Subscriptions and use the 'Add' feature to access the link to the free trial form. It should now open with the correct details displayed.