Old trick...
1 - Cut 2 X 2cm squares of chamois, make them just slightly damp.
2 - Find a socket that is about 1mm larger than required (it should just slip over the lock nut).
3 - Place Chamois square/squares over front of socket.
4 - With a rubber mallet (preferable) push the socket and chamois over lock nut (use some force)
5 - insert breaker bar and turn. As you turn the chamois will bite into the lock nut grooves.
PS - you may need only one piece of chamois or maybe three. Depends on the socket....