I called 1-800# again today regarding biometric appointment letter. The lady informed me that 1-800# is a national USCIS number and it doesn't send out biometric appoinment letter even if there is confirmation number in the system. I then asked her if it's possible to notify local ASC that appoinment letter is not required. She said that she will record the problem in the system. She sincerely wish the issue can be resolved in the next few weeks. She also recommends me contact local USCIS office to report the issue. Local USCIS address is on the lower left side of the I485 approval notice.
It seems that there might be a solution to biometric appointment letter soon if enough people bring up the issue to 1-800#, local ASC, and local USCIS office. I'll drop by San Jose, CA ASC again tomorrow afternoon to see if I can report the problem to the office manager.
Last time, the guard at the door told me firmly that appointment letter is strictly required and local ASC can not do anything without the letter. He suggested me sort things out with USCIS.