Well, the prize for pointing out my stupidity goes to CaptainSarcastic. Since my download speed always used to be so good, I never paid attention as to where I was downloading from: I know it's a respected institution, but the Sorbonne is in France (Jussieu), which is where I was downloading from! I certainly did not go there deliberately. I just downloaded 2011.09 in 7 minutes from heanet at 1.3 MegaBytes/sec How I could have been switched to France is still a puzzle to me.
The TWC agent last night had me do a traceroute in their chat room, but I could not copy it to her because I was for the first time in my life on Winders7 and some bing function kept wanting to be installed. That was also the first time I saw a traceroute result and didn't quite know how to interpret it. I take also back all the dark thoughts I might have harbored about TWC. In the process, my modem has been reset, my router still works and I can go on replacing W in my new VAIO
Thanks very much for all your help,