Disc brakes feel spongy no matter how much I bleed them

Proportioning valve is stuck? Or the Master cylinder push rod to long or short? I had a car come in that left they the shipping tab on the master cylinder instead of installing the ring and boot if equiped with one. Instead of a C-clip. The piston was relying on the brake switch and was coming out to far. You need to diagnose and fix this yourself. We are all just guessing without inspecting your work and or parts used.