at command not responding on sim800L and arduino uno

I would like to ask around SIM800L EVB module to sending message using Arduino UNO R3 DIP/SMD CH340. i change the pin tx/rx from 2, 3 vice versa, 7,8 the result either not displaying anything or anytext, the serial monitor just displaying AT no respon from the SIM800L EVB module. pls enlighten me. thank you

Schematic for both describe below:

SIM800L EVB:

Arduino UNO R3 DIP/SMD CH340:

AT Command not displaying anything/anytext:

The code from here I modified the pin as below

#include "SoftwareSerial.h"

SoftwareSerial SMS_Gateway(0, 1); // Rx | Tx
char tempChar = "";

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println("Testing the SIM800 Module");

  SMS_Gateway.begin(115200);

  for (int i = 0; i < 10; i++) {
    Serial.print("=====");
    delay(500);
  }
  Serial.println();
  Serial.println("Starting Connection");
}

void loop() {
  // put your main code here, to run repeatedly:
  if (SMS_Gateway.available()) {
    tempChar = SMS_Gateway.read();
    Serial.write(tempChar);
  }

  if (Serial.available()) {
    tempChar = Serial.read();
    SMS_Gateway.write(tempChar);
  }
}

From your images I see that you wired the Arduino Rx to the SIM800 Rx and the same for the Tx but the color is hard to see. You need to wire the Arduino Rx to the Sim800 Tx and the Arduino Tx to the Sim800 Rx. This means that the command send (Tx) by the Arduino is received (Rx by the SIM800) and visa versa.

Also connect your Arduino Gnd to the SIM800 Gnd unless you are sure they share their ground through the power supply.

The SIM800 automatically matches baudrates so keep sending AT commands until you get a OK back.