A new replacement bracket is £51 which is a bit steep for a bit of pressed steel but not the end of the world.
I would have given up after 10-15 mins of attempting to extract the remaining section.
Got the grinder out and welded on a new nut.
Even my shitty welding skills are capable of a couple of tack welds with an arc welder.
(The mrs only recently told me she learnt to weld in year 9 D&T.
They didn't let us near anything like that in my school- the teachers knew us too well.
That may be why she's got a degree and a career and I'm the thick one running a shop and setting peoples garden furniture on fire
)