The full story of the foulup goes like this. The ur-mistake was mine, due to my change in email address earlier this year. I notified everyone I could think of, and monitored close to six months of email leading up to that, but apparently the ISP didn't send me anything in that time, so I hadn't realized that I needed to change the email address on the account.
On the flip side, I was certain that the account was auto-renewing, and in fact the site itself *was* auto-renewing -- but they apparently have completely separate policies, flags and schedules for the site and domain. So while the *content* of jducoeur.org was paid-up, the *domain* wasn't. And presumably, when they tried to send me a notice, it went to a dead email address.
This morning's confusion was because of two problems at the ISP end. One is that, when the domain has expired, they make the results singularly random. Sometimes, it was going to a page that does say (at the top, now that I'm looking closely) that the site has expired. But for most of the day, it was simply redirecting to all sorts of randomness, with no rhyme or reason. So I ding the ISP for making the situation exceedingly confusing.
Second, and worse -- when I *did* try to renew this morning, their UI informed me that the domain was no longer under their control, and that I would have to transfer it back to them to have them manage it. This was why I was convinced that someone had stolen the domain.
But in fact, it was apparently their own computers screwing up. They did get back to me (via an email still sent to the wrong address, but I found it in the management interface), telling me that they still had control of the domain, and I should renew -- duh. So I wound up on chat with their support people, who took the better part of half an hour to figure out what was screwed up and fix it so that I once again had control of the domain, and finally *could* renew it.
Anyway, knock on wood, I think the crisis is averted. It depends on the network -- my desktop machine is still showing a spam site, but my phone is showing the real one. But I believe I am spared from having to track down hundreds of sites and asking them to change their links. Thanks again to the cooler heads who pointed out that all might not be lost yet.
(And while the ISP eventually acquitted themselves enough that I will probably leave the site there for now, I do think I'm going to switch the domain to my usual NIC sometime soon...)