maybe try accessing it via: https://myaccount.tpg.com.au/ if you have an account?
if you haven't logged in for the first time, try entering the username as your mobile number and click forgotten password, it should really then shoot you an email for you to reset it.
Here is an article that you may find helpful. Please see the links below.
Let us know how it will go.
Hoping someone can help out I've been with tpg for a few months now but I don't seem to be getting an actual bill sent out telling me when my bill is due I'm just guessing at this stage from when it was taken out of my account the month prior