If nothing works and you don’t hear it working you might need to take the CD changer cover out while still connected to the wire harness to find out if something has stuck the internal mechanism and if it is actually working.

I had that problem with my original CD changer but unfortunately some plastic pieces in there were already broken so there was no fix for it anyway. It served me to to learn how this changer worked (As if it's useful at all to know ) and it ultimately was the only way for me to get my CDs back.