putting my 2c in .....
Idea #1 - Using oxy heat said bolt untill it just begins to glow and rapidly cool down ( repeat process 5 times then try)
idea #2 before u rounded the bolt did u try using a punch and 4pound hammer to shock the bolt before u tried to crak it, this usually works if u haven't try hitting it then put on a open ender of smaller size if its f**ked or try a pipe spanner
Idea#3 push the car off a cliff and hope the shok makes it come loose