Antenna Replacement Help Needed...

My antanna snapped off above the threads; thus, the threaded portion is still "in".

I've considered replacing the entire assembly (below the fender and up), but really I just want to pull the thread portion out to save some coin.

I've attempted to drill out the threaded portion, but it just spins around in there when I get the drill on it. Further, I can't pull it out with a magnet.

I'm out of ideas (other than replacing the entire assembly); anyone else addressed this issue? All constructive suggestions appreciated.

 

The broken off portion is just spinning down inside where the threads reside?
Maybe, without looking at it of course there is a nut on the backside? Might need to drop the splash guard out of the wheel housing and shin a light in there.