The existing visible threads are all of 1/4 inch or less of space to grip. The problem previously, as has been stated, is that there was never enough proper grip. Every attempt simply sheared more material off, hence moving in a different direction. Flat edges for grip with flat edge tools. Trying the pipe wrenches after grinding flats was an attempt on a slightly better surface to actually be able to tighten the jaws enough to not simply slide around or shear material.
I can't speak for everyone but I never realized
wrench flats were only 1/4th inch deep to begin with. Was that clear at the onset? If all nuts,bolts and plugs only had 1/4tr inch of flat,few if any tools,including late night infomercial tools would work if stubborn when it was new,much less after it's buggered up. It's no sin or crime to hire someone with more experience and tools.