You may try the basic troubleshooting steps below:
1. Turn off/on your mobile phone to refresh.
2. Check your SMS center number, it should be +61415011501
3. Try different mobile phone to check if service will work.
If all else fails, kindly provide us the error message that you are getting.
Please send us a private message with your TPG customer ID, username and complete address so we can pull up the account and further assist you.
To send a PM, please refer to this link: How do I private message (PM) in the community