Lower control arm bolt

So I was changing the lower control arm earlier and snapped the welded nut inside the body, it's the one near the rear side holding a bracket over a bush, now the bolt just spins, I've had a look under the carpet in the passenger footwell and I'm not sure where I would need to cut a flap to get it out(if I need to), anybody else had to deal with this before that can give me some tips?