Rear Brakes

[vinny]

hello just been changing rear brake pads on my galaxy done left side(so true in what you say with the tool it was easy.starting doing right side the disc look really rusty but i still carried on undone to 13mm bolts push the piston back with tool but the 2 bits where the bolts screw in to were seized(not moving at all)so spayed wd40 tried moving it but bent one side.what this part called how much and is it just undo 2 big bolt sat bottom and take thing of as i probaly change disc aswell thanks