You can also try some mineral penetrating oil or WD-40, it won't hurt, but it may smell.
Had the inverse issue, I was trying to rescue the cleats from a pair of wrecked shoes. Gave it a dose, some time, removed the gunk, and was able to budge the things.
Use water to loosen the mud etc. then pick out the gunk and stone fragments with a pointy widget.
This was a favourite of mine on (usually) c/sunk screws. The contact surface area between bolt and meal is large but the hex is smaller than a normal bolt so they can be prone to seizing...pretty much like cleat bolts. You'l need to hold the shoe as steady and tight as possible though or the impact gets lost in the movement.Failing all the suggested you could try placing a centre dot punch on the outer circumference of the screw and tap in an anticlockwise direction with a small hammer whilst holding the shoe in between your knees.