I'm guessing you're working on the shock mount? Can't really imagine them being very stubborn. Of course, it could be because I skipped the spring compressor and it couldn't wait to pop off and try to shoot the nut across my garage.
Do you have the assembly out of the car? My suggestion would be to make sure the top nut and washer are safely out of the way, release the tension on the spring compressor so the spring helps, and use a rubber mallet / block of wood and a hammer to beat on the top bolt until the mount pops off.