I'd suggest double-checking the FPC plug going from the USB port to the motherboard. If it's not fully seated you could conceivably be getting power connections but not all of the pins making contact meaning the data connection's not working. Unplug it and check both sides for bent or broken pins; use a magnifying glass and a bright light. Bent pins can sometimes be straightened with some fine tip tweezers, but of course broken ones are more problematic.
Clean both sides with 90% or higher concentration of isopropyl alcohol and reconnect then see if it's working before you button everything back up. If it's still not working and you still have the original port, try plugging that one back in and see if the problem persists. If that fixes it, you'll need to get in touch with the iFixit Store people for a replacement part. I know they try to do their best to provide the highest quality parts possible, but it's just a fact of life that sometimes they get shipped a bad apple.