BMW Repair: o2 sensor replaced twice, o2 sensors, computer reset

Question
98 BMW 318I  The O2 sensors were replaced twice by mechanics professionally.  Check engine light is still on (even after mechanics said computer reset and car driven) and still reads O2 sensor not working when hitched to computer.  Been dealing with this for almost a year and the car  still can't pass inspection due to this. Do you have any clue what else could trigger this or what could be checked or done? We really need our car(have a new baby)...Thanks....

Answer
I gather the only code that was recorded was that of a weak O2 sensor.The problem although the code says an O2 sensor maybe due to a cat problem,an oil leak,air leak of some kind,there can be many things that set off O2 codes,just because it came up with a oxygen sensor code doesn't mean that the sensor is bad it means that the sensor is reading incorrect information.I don't know the codes that were received,so diagnosis is difficult on my end.