On 14 December 2017, the ATO plans to make changes to their Technical help desk site to improve your experience. These changes include improved search functionality, a view of the top five trending articles and upgraded call back options that let you request a call back at a time that suits you.
Some of the services you currently use will change. After the upgrade you will now need to register to use the call back service or to submit a case for the issue you are experiencing. The ATO will let you know more about the changes shortly. For now, the registration option has been temporarily disabled.