First of all, lets get some assertions out of the way. As you have been trying different program we can assert that you have a working usb connection and can program the Arduino unit. I assume you are using the Arduino IDE. Do you use the same baud rate in the program and while communicating with the program (say 9600 or 115200)? Can you read serial communication from the Arduino if say doing
Serial.println("test");? When sending over the serial, can you echo the sent data to confirm the data you read is the same you sent? Have you checked line ending in the Serial Monitor
With those questions out of the way, confirm that you are sending data trough the
SerialSARA expands to the
Serial2 interface, you can try to write to this serial interface.
If these pointers dont work out, we can try another program before we try another approach.