Repairing electrical oven - appears to be broekn thermostat, but is not
It sounds as though the wires may be shorted together. When it comes right down to it the thermostat is just cutting or energizing power like a light switch so if the wires were to touch farther down the line the switch would be worthless. I would physically trace all the wires in the circuit to make sure they aren’t bridging the thermostat. You could take both wires off the heating element and see if you have continuity with an ohm meter. Continue up the line until you get OL and your short should be there.