Yeah, you'll need to replace those thermometers/hygrometers. They're honestly useless and I can't believe they're still sold.
Honestly, you should unplug the heat mat asap until you get a thermostat. Google search snake burns if you need to see how bad those heat mats can get.
Depending on the temps in the room the snake is in you may be better off shutting all the heat. They handle cold better than hot