Should they be getting better lines than this?
Yes, a 43dB would normally give in excess of 10Mbps.
They dont have a master socket to test that though
They probably do have a master socket (it's quite rare to have the entire phone wiring going back to one of those old hard-wired junction boxes).
What I guess you mean is they don't have the type of master with an internal test socket.
In which case, there's not much they can do.
Are all the extensions hard-wired into the back of the master (or other sockets), or do they plug into the front of the master?
Ade
ADSL24/Entanet - 20 months and counting, with Entanet!
DL Sync 4000kbps
UL Sync 448