I am having some trouble setting up Dynamic DNS with my Fritz!Box 7360.

I have set up the Dynamic DNS page with (this is translated from German, so might be worded a bit differently):

[x] Use dynamic DNS
Dynamic DNS Provider: User defined
Update-URL: https://freedns.afraid.org/dynamic/update.php?MY-DIRECT-URL-KEY
Domain Name: mydomain.crabdance.com
User Name: myusername
Password: mypassword

Now on the FritzBox status page, it says:

Dynamic DNS: activated, mydomain.crabdance.com, Status: Account temprarily deactivated

When I check back on http://freedns.afraid.org, my IP address never changes. Is there any way to fix this?

Note my router is on an IPv6 network (m-net), with IPv4 only through DS-Lite. I'm not sure whether this affects anything.

Update: Following the guide here (putting myusername instead of MY-DIRECT-URL-KEY) hasn't given any succes. However, the status field has changed slightly:

Dynamic DNS: activated, mydomain.crabdance.com, Status: unknown