I registered last week thru patek.com , no problems at all...
Not that this helps you, sorry
I've noticed that in the back of their magazines you can find a post card with an address in London and a fax number as well where you can let them know of your address change. Perhaps mailing or faxing them would help?
The address is:
Patek Philippe International Magazine Forward Ltd
84-86 Regent Street
LONDON
GREAT BRITAIN
W1E 6BW
The fax number is + 41 (0) 22 884 2547
Hope this helps and that you will be able to receive once again the magazine.
Best regards,
Alex