Oil and heat and oil again, let it cool lets the oil sook into it better. Using a 1/2 or bigger breaker bar and maybe a pipe for a longer handle. Start to turn it, if it is not moving try a different one, go around and see if any start to move. If not take a 1 pound hammer and start to tap on the bolt as you try to turn it, I tap on the breaker bar end. MAKE SURE YOU ARE USING 6 POINTS SOCKIT. I have broken a fair amount of sockets turning these. REmember to tighten them half a turn at a time , or the last one is a bear.
Good luck !!