does the remote work to lock the doors?? if not manually lock all the door ( not with the key ) then unlock either side front doors with the key this should turn the system off but will reset after you get out of the car and lock the doors,
the problem could be the remote PCB the computer board inside the key check the PCB with a magnifying glass to see if any of the tracks are broken
if system is still live and wont turn off it could be one of the door courtesy lights are blown check each one by opening the door and closing it the light should come on when open and go out when shut, any light that dosnt work will cause your symptom