An update on our on-going nightmare with AT&T: after two weeks, four technician visits to our house, and I don't know how many phone calls to CSRs and supervisors, they were finally able to get our internet connection back up and running today.
That's the good news.
The bad news is that somehow they managed to break our phone line in the process. It was working this morning, but just as the internet tech was leaving we noticed that we didn't have a dial tone on our main phone line any more. We've been down for a few hours now and they have not been able to figure out what the problem is, except that as far as anyone can tell, the problem is far upstream of our house, and the fact that it happened at the same time that we were fiddling with the internet connection is just a coincidence.
But it's a damned odd coincidence. Damned annoying too.
[UPDATE:] They fixed it. Whew!
[UPDATE March 12:] The nightmare is not over. They are still billing me for my now-discontinued DSL service. On hold with AT&T billing for 30 minutes and counting while they (supposedly) fix it... arrggghhh!!!