1995 Taurus Rear Disk Brakes with ABS

Trying to put new rear brake pads on 95 taurus with ABS but cannot compress the the caliper cylinder. I bought the special tool which is supposed to turn the piston but it still does not budge. I tried opening the bleeded but this didn't help either. What is the trick in or to compress this piston so I can get the caliper over the new pads?

They might be frozen due to corrsion or rust. Happened to me. Treat it like a rusted bolt. Spray WD 40 around the piston, let it soak, light tapping with a hammer, work it back and forth. You know the drill. Worked for me, good luck.