I suggest that you use Serial Monitor for the debugging (if needed) of the Arduino side of things; once you're confident that that works correctly, start working on the simulink side of things.
Be aware that when opening the serial port on the PC, your Arduino will be reset and you will have to wait a while before the PC will see data coming from the Arduino.
Further, as Mrs. Drew pointed out, you have a far better chance at a forum dedicated to simulink; there are probably not that many simulink users here.