Having made no progress on this issue, here is a letter that I sent to the Prime Minister:
Dear Prime Minister
Since June 2016 I have been unable to access my son’s myPlace webpage via the myGov website.
I have raised this several times. Yesterday, I spent about 2 hours mostly on hold with the NDIA and the myGov helpline.
The NDIA said their system is working perfectly and that the problem is with the myGov website. The myGov help people check out their system and said the problem is the NDIA’s myPlace system.