Welcome to the Community!
We were able to locate your account and the plan that you are in is the NBN12/1 speed tier.
The speed that you are getting is within the specification of the said plan.
If you are looking for a higher speed, then you may upgrade to our best selling NBN50 speed tier plan that has a typical evening speed of 46.0 Mbps.
Here's an article on How to Change NBN Plan Online via TPG My Account.
Are you using a WiFi or a Wired connection? We've created some articles that will guide you on how to improve your home network.
We've also created an article that will guide you on how to troubleshoot a slow speed issue.
Let us know how it goes.