Wait :-) There are several things that can make a postcard take a long time to be registered. Here are a few:

• slow postal services;
• the user is on holidays;
• the user does not have a home internet connection;
• user didn't understand your handwriting and is trying to figure out the ID by contacting us;

And no, there isn't anything we can do to help you on that. Please be patient, experienced postcrossers will quickly advise you to do the same - it works! :-).