Before changing the sump get a bar welded to whats left of the nut you have got nothing to loose, you could also grind the head off once removed it releases the tension on the sump plug and it should come out. It is the surface area of the washer that makes them tight not the thread. People use the wrong type of sockets when trying to remove them always use a six sided 1/2" drive socket impact type they sell them singularly at Halfords.
Some places suck the oil out via the dipstick hole like you would on a marine engine.
Dont despare there more than one way to skin a pussy
Thanks for the info, T:
Yes someone has offered me a marine oil suction pump, so i might give that a try.
The sumps are so expensive i have only just brought the van and it only had a service this time last year, so how they got the oiol out i don't know.
unless the thread has sripped and they have loc tighted the bung in