Lambda sensors and readiness code

Hi,

I have a skoda fabia 2005 model , 1.4l engine.

Some days ago I found engine light on, so went to service company.

They told lambda sensors are broken, so changed both the sensors.

Still light is ON, they could not reset the errors with autologic.

They are telling updation of software is needed.

If someone guide me how could be the reasons and what to do.

Error code, I have seen was 16421 and 16415.

Thanks,

BT