When you cancelled your tpg internet, did you convert to email-only account? If not, all your emails may have been deleted. POP3 emails are deleted after 45 days anyhow. Better to use an email client which downloads emails to your computer/wifi device.
You could send an email to firstname.lastname@example.org detailing your situation.
As I understand it, your new provider contacts NBNCo to make the changeover. Your new provider might provide an email facility but it will be separate from tpg email. TPG can't block emails to your new address.