Two serials can't work on the same speed
I spent some time playing with your code and it seems your code actually loops the serial therefore if they are both set at 9600 as example and you print what the other one is sending like in your code you end up in a loop if you want to read what your serial is sending it is better put that values in a variable and send it 

if you load your code you will get the following message in the arduino IDE once you try to connect to the serial monitor:

Error opening serial port 'COM8'. (Port busy),

your port is busy because the one serial port is reading the other all the time 

one more thing I would use the following if you want to repeat a serial port:


 
  if (mySerial.available()) 
  {
    //char c = mySerial.read();
    Serial.write(mySerial.read());  
  }


Hope this hels you