I cannot get the nut/compression nut off
MORE info needed.
what inlet nut?? On the shutoff exit? or the tank filler vavle under the tank?? OR do you have compression BEFORE the shutoff? ANY nut that doesnt come off here,,,gets "2" hammers tapping at same time from BOTH sides at once and tapped around as far as you can,,,that USUALLY knocks the crap out of them and loosenes the thread,,,same thing for pipe fittings and threaded pipe etc.!!! hasnt failed to work yet,if not successful, try try again!! Care must be used to govern tapping force to type and size of pipe etc used on,,,dont egg fittings your planning on using again!!(or unscrewing for that matter)
AND what type of pipe are you using(working with)??Are you SURE its threaded?? When all else fails,,, a hex sided line wrench works wonders over a 2 surface open end wrench