Cut the line and use a socket wrench.

You’ve still got a fighting chance if you stop now and get a line wrench on there instead of whatever you’re using. Also called flare nut wrenches

heat,lube,heat,lube then vice grip.

Grab with vise grips try tightening a little first then try to loosen. Like said cut off n use socket n heat

Penetrating oil (such as PB Blaster). A MAP torch (seriously). And a flare nut wrench. Do not use channel locks, box end, or adjustable.

Flare nut wrench

Used the wrong wrench to start…need line wrench

Get it red hot with a torch, let it cool, use the brake wrench thingy