2004 Mitsubishi Galant o2 sensor.

Engine Mechanical problem
2004 Mitsubishi Galant 4 cyl Front Wheel Drive

i've chagned the o2 sensors on my car and the check engine light still does not com eoff.
I've had it turned off twice.
and still the light refuses to turn off.
I want to pass the smog in mass and want to know about any ideas to help fix the problem.
desperately seeking help.