Hello Benjaminp,
I have had the same problem, waited as long as you have on many downloads, and that's with a 'better than T3' connection! I know your frustration and can readily see that your request for help has not been met yet.
I got some, though not full, satisfaction from some assistance that Lord o' de Ring gave at
this thread, though even some times after using that method, it still doesn't resume at even the perecentage at which that last save of backup files was made. Almost always, for me, it starts at 0%, not 10% or 20% or any other %. His recommendation surely made a difference on all those losses I regularly experience, still, though is not always the solution. Give it a try for all it's worth, it's helped me.