We apologise for the wrong information.
We've checked the account and can confirm that you are under our NBN business FTTC bundle, which includes a static IP address.
It is available when you log in to "My Account", then under NBN account management click on "ADSL Settings". On the page, look for the WAN IP address.
May we know where did you notice that the IP address was changed?
Are you able to send a private message with the screenshot of the IP address change?