The text message came through from the Victorian Department of Health and Human Services (DHHS) at 12:25pm on August 6.
"Dear Alexander, unless you have been re-exposed to COVID-19 or you are waiting on test results, you are no longer in quarantine."
The year 12 student and his mother, Anna Perri, were "mortified" — because, they say, they didn't even know he was supposed to be in quarantine at all.
"It just was a great shock, because it potentially could have put us all at risk," Ms Perri told ABC Radio Melbourne Mornings.
When Thornbury High School, in Melbourne's north, was closed in mid-July due to a case of COVID-19, parents were told they would hear from DHHS if their child was required to quarantine.
"When we didn't hear, we believed that we weren't a close contact, so we went about doing what we normally do under the restrictions," Ms Perri said.
The family was "shocked and horrified" to learn Alexander was found to be a close contact two weeks after he had been exposed to the virus.
"We should have known immediately so we could take appropriate steps," Ms Perri said.
"The thought that he could have put me at risk — or other people at risk — was really distressing for him and for me."
At Friday's daily update, Victorian Chief Health Officer Brett Sutton said contact tracers had been able to get the message out to "virtually 100 per cent" of close contacts within 48 hours.
"When cases are at 50 a day or 50 a week, everyone in the world was doing contact tracing to the nth degree," Mr Sutton said.
"When you've got 300, 400 cases a day, that stretches any system anywhere in the world.
"We are doing much better than a whole bunch of countries that gave up on contact tracing."
Meanwhile, Sarah, who shares a house with a positive coronavirus case in Glen Iris, called the ABC to say she had also had problems with contact tracers.
"We are now on day 10 of our quarantine and isolation, however only two of [my housemates'] close contacts have been contacted by DHHS," she told Virginia Trioli.
"Every day I am sitting by the phone waiting to be contacted to get the right information.
"[I have] received no information about how to properly quarantine or anything, other than what I've researched myself."
She said she was "worried and frustrated" by the lack of information.
"Whenever I've called the [coronavirus] hotline, I've been given different information or been sent in circles with numbers that don't connect to anywhere."
