HC-12 AT Commands not working

Question

I'm currently working on HC-12 transceivers. Normal operations are fine and I was able to successfully transmit basic strings between an Arduino UNO and and Arduino Nano, both of which use HC-12s.

However, when I'm trying to configure the HC-12s using AT commands, the commands that I send through the serial monitor, like the basic "AT" or "AT+VERSION" return no response.

Here's my wiring setup

1. HC-12 VCC to Arduino 5V
2. HC-12 GND to Arduino GND
3. HC-12 RXD to Arduino D11
4. HC-12 TXD to Arduino D10
5. HC-12 SET to Arduino GND

And here's my arduino code fore sending AT commands

#include <SoftwareSerial.h>
#define RX 11 //Connect to the TX pin of the HC-12
#define TX 10 //Connect to the RX pin of the HC-12
SoftwareSerial mySerial(RX, TX);
void setup() {

  Serial.begin(9600);
  mySerial.begin(9600);
while(!Serial);
Serial.println("Input AT commands");
}
void loop() { // run over and over
  if (mySerial.available()) {
    Serial.write(mySerial.read());
  }
  if (Serial.available()) {
    mySerial.write(Serial.read());
  }
}

Things I've already tried include switching to different baud rates from 300 to 9600. I've also tried the HC-12 GUI configuration tool, but that one returns an error "Serial I/O error: CreateFile failed"

Is there any way to find out if this is a problem of the HC-12 itself, or just a configuration issue?