Very likely the resin is fouled or has failed.
If you have iron in your water iron fouling is very possible--particlarly becuase the regeneration is apparently not working. The fact that brine tank fills indicated that there is a problem internal to the control head--possible bad flappers. A rebuild is indicated.
If you are on a chlorined municipal supply chlorine may have degraded the resin. Check by taking a sample of the resin and press between your fingers. If it is mushy it has degraded. If the resin beads are hard they are probably ok.