Enables the selected software serial port to listen. Only one software serial port can listen at a time; data that arrives for other ports will be discarded. Any data already received is discarded during the call to listen() (unless the given instance is already listening).
SoftwareSerial has some limitations when you have multiple SoftwareSerial in your Arduino code: https://www.arduino.cc/en/Reference/softwareSerial.
According to: https://www.arduino.cc/en/Reference/SoftwareSerialListen