Does "internet support" exist?
 

I'm trying to reach the internet support folks from the US (1-888-962-6688). Three times in the last two days I have been on hold for 20-30 minutes before giving up.

I already booked a flight but didn't use my registered user ID when I did so. I want to see if they can attach the existing reservation to the ID so I can pull up the reservation online.

If you mean the eService Centre then yes, but the hold times can be significant sometimes. Once you get through then in my experience they are very competent and efficient.

However, that number isn't one of the ones listed on the Cathay Website as a contact number for the eService Centre. Try calling +800 2747 2200 (may well not work from a mobile, but should do from a fixed line).