2006 Corolla P0420 Trouble Code

My 2006 Corolla (168000 miles) had check engine light come on. Trouble code P0420 detected. Replaced both O2 sensors and trouble code still came on. P0420 code again. Erased code and took in for OHIO e-check. They knew codes were erased and ran dyno emissions evaluation on car. Emissions passed with a lot of room to spare. Code continues to come on even though emission test passed. I'm not planning on replacing anything else unless someone has some suggestion on why the trouble code continues to show up.