Also had this problem with talk talk, changed the modem then kept being told that it was a problem with the phone line and even though phone calls were fine. Kept being told to move nearer to the phone line, (which is in the kitchen), kept telling them I didn't want to as it would be inconvenient and if the connection had been fine in the living room for two years why shouldn't it be now.
When talktalk had a stand in the local supermarket and my husband complained to them, (it's easier than phoning). To give them their due they checked up and said it was the outside phone exchange connection that was the problem rather than the line in our house, the connection has improved since then though, although it's still not the best connection in the world as it can be a bit slow when watching bbc iplayer.
I don't know that this helps with your problem but I think it helps to know that your not the only one, I'm glad to hear I'm not. The only real advice I can give is to keep on complaining and could you me know if your computer engineer can shed any more light on the problem.
Jean
ps meant to say I'm also using an ethernet connection
