I thought I'd already activated my account the first time I got a notice about it.
The second time I got a notice, I logged in. I didn't see anything about activating...it was just a normal login. I did notice that the billing address was wrong. (It should not be the same as the service address.) I fixed it.
Today, I got ANOTHER notice about activating. I logged in again... This time I noticed that the billing address reverted back to the service address. I changed it again.
What's up with these activation notices? Do I need to do something else? It's not obvious. I did a search for activation and it showed the process I went through originally.