Hi Karen
Can you confirm if you don't write to the status register with ZXTOVx bits set to 1, involuntarily, before reading the register each time? If you did write it, that could explain why the ZXTOVx bits always reads 0. I would recommend you to write a simple code to power-up the IC (when no voltage signals are applied) and check the status register to see if the ZXTOVx bits are set? You can then write the status register with the ZXTOVx bits set to 1 and read the register continuously to monitor if these bits are set again.
Regards
hmani