Unscrew the grub screw completely, it might still be holding the bracket even though you have unscrewed it a bit.
They just spin in their sockets yet gravity will not drop them out. Infuriating.
Have you tried getting something to lever it off? You could even try a pry bar or similar as long as you have a piece of card or thin ply between it and the tiles.
Concerned about prying out the entire thing and ending up with broken tiles.
Reckon hack sawing the accessory to bits might be less risky on the assumption a direct replacement or three could be sourced. Hah.
@Bobbo started
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They just spin in their sockets yet gravity will not drop them out. Infuriating.