Forget the line wrenches.. if it doesn't easily break loose right away- stop with the line wrench and go straight to vise grips. Works every time. "Vise grips?" That's the wrong tool!". It works.. that's all that matters. If you keep using the "right" tool you'll have nothing left but visegrips as your only option, since the nut will be rounded. Just use the vise grips now and avoid rounding the nut.