Problem arduino uno sketch and sim 800l modem - sim800l

Question

The code works ok on the serial monitor and I can ses in the serial monitor that the code makes the AT command for sending a reply by sms but it doesn't send and I can't control the sketch by SMS.
I can't figure out what goes wrong. It's a long sketch so I try to set the parts of the code where the code is for the modem.
#include <SoftwareSerial.h>
const uint8_t rxPin = 2;
const uint8_t txPin = 3;
SoftwareSerial sim800(2, 3); // SIM800L rx og tx til pin 2 and 3
#define sim800 Serial
void setup() {
Serial.begin(9600);
while (!Serial) {
; // Wait for serial monitor to open
}
sim800.begin(9600);
while (!sim800) {
; // Wait for SIM800L module to start
}
sim800.println("AT");
delay(1000);
// Read response from SIM800L module
while (sim800.available()) {
String response = sim800.readString();
Serial.println(response);
if (sim800.available())
{
String message = sim800.readString();
Serial.println(message);
message.trim();
message.toUpperCase();
if(message.indexOf("ARM") >= 0) // ARM DISARM COMMAND
{
if(message.indexOf("DISARM") == 0)
{
armed = false;
send_SMS("DISARMED!");
void send_SMS(const char *message)
{
sim800.println("AT+CMGF=1"); // Set SMS mode to text
delay(100);
sim800.println("AT+CMGS=\"[phone]\""); // telefon nummer
sim800.println(message);
sim800.println((char)26); // send SMS
I can't figure out where the error is.