It sounds like you cut the shaft of the ball joint to separate the lower control arm from the steering knuckle, and now you are trying to remove the piece from the knuckle, right? Tangofox007 has the right idea, put some force on it, like a C-clamp, soak it with PB, and let it sit, overnight if you have to. Keep pressure on it and then tap with hammer all around. Make sure when you clamp it you are leaving room for the stud to move and come out. Should pop out. With the other end use a drill and drill holes all around the bottom, take a cold chiesel and connect holes, pop out that piece, drive bottom of ball joint out. Now take your sawzall and carefully cut into what is left of the ball joint in the LCA. Do this in 2-3 places use cold chiesel and knock out the pieces. Clean up the hole and press in new ball joint. Good Luck.

__________________
If it ain't broke take it apart and find out why.

1983 300SD, 4 speed
1994 C280
1987 300TD wagon
1996 HD Road King

Ride in Peace Eric Peterson, Harley of Macon