Sorry... now I see that you want 0,0 V at the output. That´s why you put the -Vcc of U3 to ground. Well, it is not possible to the output goes to 0,0 V because the saturation voltage of the internal output transistors of U3 (nearly 1,0 V above the -Vcc voltage applied to U3). To get an output voltage near to zero at the output of U3, you can connect the -Vcc of U3 to a voltage near to -1,0 V. This can be achieved with this circuit:
(-12,0V)----\/\/\/\----|<|---|<|-----(gnd)
The resistor is 1K(1/8W) and diodes are 1N4001. You must connect the -Vcc of U3 at the point where the resistor connects the diode. At this point, the voltage is near -1,2 V which compensates the saturation voltage of the OpAmp and the output for a logic level zero will be near to zero volt (in fact, around -0,2 V).