Stuck axle freehub nut

Hi guys,
Wondered if anyone could advise please? Under covid restrictions I'm finding it hard to get my bike looked at. It's only 6months old but taking it to Halfords they seem to think I have a manufacturer fault with my freehub/axle with it griding or making a noise. As it's not their range of bike they suggest I get the manufacturer to replace.

I have booked my bike in to be fixed with another local bike shop but that's still over a month away. So i thought I would look myself?

I can take of the cassette and being faced with two 17mm nuts either side of the wheel using the cone spanners I attempt to undo the cassette (and needed side) but and typically the non cassette side nut undoes and for the life of me I can't get other nut undone so i can remove the free hub to at least look inside at the bearings and even clean and apply new grease.

Is there another trick I can use to undo this freehub nut please? Cheers