That's why you should engage Customer Service directly.
As a paying customer you should have some rights.
And with the evidence to back it up, hopefully a light at the end of the tunnel.

Another option is to migrate one of you two to the better ISP.
Thus, you shouldn't be hopping out of their cloud.

But if your ISP runs a monopoly in your area only and in your brothers area it is another ISP that have their own monopoly, then it is possible that one ISP would lease the line from the other.

If I may add a suggestion, exercise yourself!

In the Bible at Luke 18:3-5, there is an example of someone getting justice from someone unjust simply by persistence. You can write to counsellors/politicians, make their name stink on social media, warn everybody against them if you can't change. But if your "broadband" is coming to you via 10km of phone cable,, that's another story.

Does Starlink have a presence in Oz? Starlink is Mad Elon Musk's Internet offering, low earth orbit Sattelites. I hear it's fast. You could even get a pricey feed & offer service to local businesses to eliminate your cost .

Not sure what some random bunch of nonsense written and updated over time for their personal gains by a bunch of rock spiders has to do with OP's internet connectivity.

OP please close this thread before the zealots take over and start spouting nonsense.
I'm out of this one.