This was the single bit that took the longest with my rear camera install. I first managed to break off a fibreglass electricians rod, as it got wedged in when pushing up from the bottom. It became jammed solid, and the more I pulled the more it jammed in between the inside and outside panels.
No joy either trying to push anything down, as I couldn't get anything round the bends at the bottom.
Did it in the end with a wire coat hanger from the bottom, and pulled it out of the hole at the top of the tailgate with some needle nose pliers. Lots of swearing involved throughout.