sounds like the rod to unlock it has come off
i had this proble so all i did was drop down the back seat and managed to remove the shelf
i then measured up 2.5" from the bottom of the tailgate and drilled a 24mm hole in line with the lock mechanism through the plastic trim this enabled me to get a finger in and open the lock
i then fitted a grommet into the hole so if ever it happened again i could still get the boot open