What is the temperature of the room that the cage is in?

Are you aware that heat mats require a thermostat to regulate their temperature to safe levels, and a probed thermometer to monitor cage temperatures?

Heat mats only heat the surfaces of the cage they come in direct contact with. They do very little if anything for the air temperature in the cage. If the room the cage is in drops below 75 F a heat lamp will probably be necessary with or without a heat mat as well.