SIM800L- Do not send messages to other phones

Hello, I work with a SIM800l, and this gives me a little problem with sending messages to another phone number, my code is this, I extract the phone number with "substring ()", the problem is not in the shipment, Since the messages to my phone arrive perfectly, the problem is when another phone sends a message, it does not receive anything, and on the arduino serial monitor it tells me that the SMS was sent correctly

  if (SIM.available()) {

    Comando = SIM.readString();
                        
    Serial.println(Comando);

    Numero = Comando.substring(9,20);

    Serial.println(Numero);                     
     
       if (Comando.indexOf(Clave) >= 0){   
           
        SMS("Recivido correctamente");   
                               
        Comando = ""; 
                             
       }else{

         SMS("ERROR: Clave y/o Comando incorrectos"); 

       }

    }

  //Serial.println("esperando comando");

  delay(250);

  //updateSerial();

}