2001 Honda Civic LX 4DR P0420 Code Not Clearing After Catalytic Converter and O2 Sensor Replacement

I own a 2001 Honda Civic LX 4-door automatic model. Recently, I received the P042-0 diagnostic trouble code (DTC), indicating a catalytic converter efficiency problem. I had both the catalytic converter and oxygen sensors replaced recently. Immediately after completing the work, the check engine light reactivated. I have since replaced the fuel filter, air filter, and spark plugs to rule out other issues. Despite these efforts, the P0420 code persists and will not clear from my vehicle's system. My upcoming inspection is at risk due to the ongoing check engine light. Can anyone provide insight into what might be causing this issue? Any suggestions or known common causes for a recurring P0420 on this model would be greatly appreciated.