I think you should get in touch with Susan Ward.
http://boards.immigrationportal.com/showthread.php?t=96693&page=80&pp=15
She had a problem with the US Consulate London
losing her I-824 Cable notification which was sent from
the Texas Service Center USCIS.
Another thing, I would advise you to contact USCIS
Customer Service to re-send your I-485 approval
details to Guangzhou via
fax because it is safer.
And ask them to send you a copy of the fax as
proof of them sending it to Guangzhou.
Normally, USCIS sends a cable telegram to Guangzhou
subsequent to the approval of your I-824. But being such a
poorly run Consulate, I suspect telegrams are often
misplaced.
Last resort is to talk/write to Stephen Fischel who is
the Director of OFFICE OF LEGISLATION,
REGULATIONS AND ADVISORY ASSISTANCE
in the Dept of State. He oversees the application of
procedures in US Consulates across the world.
Ask him to push the Guangzhou Foreign Service
officer to use a VISAS Badger to obtain your
information since your I-824 cable was misplaced
by VSC and/or Guangzhou. Here's his address:
Director: Stephen K. Fischel
OFFICE OF LEGISLATION, REGULATIONS AND ADVISORY ASSISTANCE
Room=L603E Office=CA/VO/L Location:SA-1
2401 E Street NW, SA-1,
Room L603E
Washington, DC 20522-0103
Fax: (202) 663-3898
Phone: (202) 663-1184
Good luck and tell us what happened.