My bmx seatpost is stuck into my frame HELP!?

Well I have a United Recruit BMX and my seatpost seems to look like its been hammered into the frame, the seatpost is more like a 'v' so it can be hamered in properly, i want to change it to pivitol but can't i've tryed banging it with a hammer and numerous WD-40 sprays into the frame/seatpost but still no movement, i don't know what the right thing to do to take it out is, can anyone help me D: