Loosen lock nut on rear axle T1n

Hi
Can anyone advice how to loosen the lock nut on rear axle so I can replace bearings and oil seal. This is on a 1999 412d sprinter.
I have made a tool and a long pipe but that does not move it.Apparently it is tighten to 450 Nm and with lock tight.
Please could you assist

That is about 330 ft/lb. A good air impact wrench with a 6 point impact socket would be your best bet.