This might help. I used to get a message box during long downloads which said that no activity had been detected (!) for several minutes and that the line would be disconnected in, I think, thirty seconds. Below this was a "Stay connected" button. Near the bottom of the box was a tick-box against words like "Do not use auto-disconnect". I ticked that box and have had no trouble since. (I don't understand how the system can say that there is no activity when data is pouring over the line.Perhaps it means keyboard activity?)
This thread is now locked and can not be replied to.