Okay, time to begin to divide and sort!
I might question when you say the selector is on fill, pump is off and no water inside?
Should the selector not be to the other position to get water when pump is off? Different labels at times but "fill" would mean fill the tank to me, so what is the other option for using water?
I might ask first if you are certain that water is getting through the hose. I know the regulator is saying pressure but I have little trust, so I might try backing the hose connection off just enough to see a little water come through to that point.
Maybe a gopher built a home in the hose?
If water is getting to the hose connection about the next point inside is the stool. No water there?
The one suspect between the hose port and stool would seem to be the selector knob!
No chance it is broken and setting half way between fill and use, so that neither moves water?
Maybe play with the knob for any strange feel or something of that kind?