You haven't tried an impact at this stage? Most people seem to have better luck with an impact wrench than using breaker bars on extensions.
If it's an air impact, make sure your air pressure is healthy, and have a nice size hose and fittings. Use the least number of socket extension possible to reach the crank nut, as any extension robs the impact of some torque.
If it's an air impact, make sure your air pressure is healthy, and have a nice size hose and fittings. Use the least number of socket extension possible to reach the crank nut, as any extension robs the impact of some torque.