Thank you for being a part of the TPG Community and your question today.
In reference to your question the minimum speed of 25 Mbps means NBN and in turn the many Internet Service Providers (ISP) have to provide a services of at least 25Mbps Upload - 5Mbps Download.
Speed tiers for NBN range from 12/1Mbps through to 100/40Mbps including minimum 25/5Mbps.
Basically an ISP cannot provide just the 12/1 Mbps package only.
Your chosen speed package from TPG is the basic 12/1Mbps package and my speed test results indicate that is what you are getting.
If you are having issues with your Internet experience it may be caused by "Bandwidth Sharing" where you have several devices (laptop, tablet, phone, TV etc) all sharing the connection. Streaming services (NetFlix, YouTube, Game Consoles etc) connected to WiFi on your speed tier can have quite an effect on your service. If your modem is close to your TV you might be able to connect it directly via an Ethernet Cable.
You may consider upgrading your service to a higher speed tier such as the 50/20Mbps plan for a better experience particularly if there are several people in the home.
Please contact us again if you consider this option.