Called support today on my mobile on the way into work, but they aid they needed to run a "line check" and I would need to be at my computer for the test.
I called back when I got home, and told them the update - all hardware working on one line, and all hardware giving the same result on my line :(
The guy on the tech support said he couldnt esculate an error 619 to BT, but I wasnt going to let this guy off the phone without some progress. They suggested that I talk to Microsoft support about what the problem was with my PC(s)
I evenually mentioned that I had noticed the bytes tx counting up, and bytes rx remaining at zero, also loss of signal, loss of frame, and errored seconds on my line. The errored seconds seemed to illuminate something in his mind, and he spoke to a supervisor, and got it esculated to BT. We'll wait and see....