i would say they will be weld captivated and they have broke free ,
unsure to be honest but i would imagine you would need the aid of a decent welder to sort it pal unfortunately
may need the top part of the box section cutting open then the captivated bolt part or lugs welding back in...
then the box top section you removed earlier welding back on ........
if this is the case will be a nightmare hope you sort it