Hello Leon
So you don't have any sockets available.
How do you get the signal from the dongle ( or whatever it is ) to your computer?
Do you have any WiFi routers that you could turn into a bridge?
Am I missing something? if a tree is in your line of sight and you are in a semi or rural location is anything stopping you from physically having the dongle in a direct LOS to the telecommunications tower and then getting the data stream to your computer.
I'm in Bathurst and just ran a Speetest on my phone ( Telstra, Samsung Note 9 ) I got a 157Mb download stream indoors. Have you tried running Speedtest on your PHONE? If your phone can get a higher speed than you are seeing on your computer then you may have narrowed down the problem.
Have you a second computer you can try - or in these social distancing days access to one you can also try.
Have you thought of a signal booster, like,
https://www.amazon.com.au/Antenna-Et...6384784&sr=8-2
Ed