Aside from the same issue occuring a few months ago, our connection had been stable up until a week and a half ago when our service started dropping out and re-connecting every 10-20 minutes. Restarting/restoring the router has had no effect and a call to customer service last weekend resulted in a Telstra outage being blamed for the issue - this can't be the case though as there are currently no reported outages.
Welcome to the Community!
I checked your case history and here's what I found:
I can see that your connection still dropping even with the new modem. I'll have our Engineering Team contact you tomorrow to discuss the next step for this case. Please expect the call between 1-2PM VIC time. Most likely, we'll be sending a TPG technician for further investigation.
Our records show that you've been contacted by our Engineering Team yesterday. Based on the notes, it was acknowledged that your connection was still dropping even with the new modem. However, you agreed to have the ticket closed since NBN is expected to be installed tomorrow (Friday).
At this point, though, it seems like your connection has been stable for more than a day already. Hopefully that stays until the installation of NBN.
Let me know if you have other concerns that we can look into.