XBT help

Employment based 485 approved 1+year ago.

I824, follow to join, was approved 3 months ago, but I have not received any documents so far.

In the I824 form, I checked C, notify Guang Zhou consulate.
In the approval notice, it just said the case has been approved. The email they sent me said: Cable sent to American Consulate or port of entry notifying them of approval.

I checked with NVC and Guangzhou visa office; they all told me that they have no record for my case. I do not know what to do next? Please give advice.

Thank you.