Ora ho telefonato a casa e mi sono fatto dare l'ip pubblico.
Ho ricevuto quindi anche la mail che mi spiega quello che è successo, ma non capisco, perchè se è come dici tu io non dovrei rientrare in questo problema.

A hostname you had registered with Dynamic Network Services, Inc. (DynDNS),
host.homelinux.xxx, has been deleted from our systems.

This hostname has been deleted a week after the last legitimate update
prior to its blocking. Our policies forbid multiple successive updates from
the same IP address for performance and resource-conservation purposes;
such updates have no function, and use resources which could better serve
others.

If you are using a hardware router's built-in update functionality, it is
most likely not properly functional; we recommend that you contact your
router's manufacturer regarding this issue and ask them to contact us for
assistance correcting their products to interface properly with our
systems. Until such a time that you see an announcement on our site about
your specific router functioning properly with our systems, we recommend
using a software client from <http://www.dyndns.com/support/clients/>
instead, and being certain to disable the update functionality of your
router.

You can re-create this hostname at your convenience, and we suggest that
you re-examine your update procedures and read our abuse policy at
http://www.dyndns.com/support/abuse.html for further clarification.

If you do not use your account any longer, please delete it using the tools
at <https://www.dyndns.com/account/settings/delete.html>. We regret seeing
you go.

Replies to this e-mail address will not be read. Please contact
support@dyndns.com if you have questions, queries, or comments.

Sincerely,
The DynDNS Team
ciao e grazie