I have sim800l module connected to arduino and i'm trying to initialize it in my setup function with this code:

#include <SoftwareSerial.h>

//SIM800 TX is connected to Arduino D8
#define SIM800_TX_PIN 6
//SIM800 RX is connected to Arduino D7
#define SIM800_RX_PIN 7
SoftwareSerial serialSIM800(SIM800_TX_PIN,SIM800_RX_PIN);

void setup()
{
  Serial.begin(38400);
  while(!Serial);
  serialSIM800.begin(38400);
  Serial.println("wait for .... it");
  delay(10000);
  

  // comments added just for example, both commands return junk
  //serialSIM800.write("AT\r\n"); 
  //serialSIM800.write("AT+SAPBR=3,1,\"Contype\",\"GPRS\"\r\n");
 
  Serial.println("command sent");
  delay(2500);
       
  Serial.write(serialSIM800.read());
}

but Serial.write return's junk.

When i use this code

  //Read SIM800 output (if available) and print it in Arduino IDE Serial Monitor
  if(serialSIM800.available()){
    Serial.write(serialSIM800.read());
  }
  //Read Arduino IDE Serial Monitor inputs (if available) and send them to SIM800
  if(Serial.available()){    
    serialSIM800.write(Serial.read());
  }

and send AT+SAPBR=3,1,"Contype","GPRS" or just AT command with serial monitor, everything works fine.

Can someone help with this?