do u have an air compressor? if so u can get an impact hammer with a chisel and try 2 spin it that way of just a chisel by itself.

Craftsman also makes "bolt out" sockets which might work

Bolt Out Set

if that fails then there are tools called nut splitters for $15 from craftsman also

Nut Cracker


Once you get it off check the threads the last person probobly cross threaded it.
That means u either have 2 get a tap and die set or for the same price just buy a new strut top hat and know that it is new and nothing is wrong with it