It sounds like you have dropped the complete front subframe off the car and now need to strip it further.
A word of warning here...if you release that bottom nut without any restraint in place that spring has the potential to fly out and kill you...!
Put the bottom nut back on at arms length and whatever you do dont hit it with a hammer , it really is that scarey .
Thread a metre length of 12mm screwed rod through the centre of the spring and assembly ,top to bottom ,with suitable sized plate washers and nuts either end . It takes minutes to fit and keeps everything safe.
They sell 12 and 16mm screwed rod in metre lengths in B&Q..From memory I think it's the 12mm you need.
You can then whack, heat, or do ,whatever you want to the bottom attachment and when it does ,"let go" the spring wont hit you .
Then release the spring tension gradually by undoing the screwed rod.
That spring is under massive compression , when you get it out you realise the force it contains.