Its a manual aerial..? try pushing it down by hand.. if its manual.. itll go down easy (providing it isnt bent)
On your dash/instrument cluster, right hand side, there should be one button to go up, and one to go down. Press the appropriate one if you have an electric antenna. Otherwise, get out of the car and push the aerial down.
Ok i think its electrical, because. When i had the car first. It came without a stereo. The arial stayed down. and when i tryed to bring it up. It simply rejected and would pull down. I'll take a stab and look at the dash... keep u informed. ta ~~ ok yeah it slid down... its just because i went to go through the drive wash.. and ma missus jumped out and tryed to put it down.. but it wouldnt go down.. ?? lol trust women.. sorry for the dumb question! ha