Ok looking at this
The yellow box looks like the master socket. If there's a socket before this then things probably aren't quite right.
It's possible that you have two masters though. Take a photo of all of the sockets in your house please. So we can see what's what.
The yellow box is so big because there's possibly an i-plate installed?
& that cheap flat white extension is probably shaving several Mbps from your current speed.
As it's flat imagine it as a giant antenna and as it passes any plug socket, electrical appliance etc it picks up that interference and the broadband speed drops.
Then on top of this the material used inside it is poor reducing the speed further.
Twisted cables don't do this.
I'm sure they'll sort things out for the fibre installation. They have too