problem in serail communication with sim908 with arduino mega

I am trying to communicate with SIM908 module with Arduino mega 2560.

Module i am using has 232 port,so i am using 232 to TTL convertor to communicate..

My circuit connections are as follows:
Rx-Tx-0, Tx-Rx-0, GND-GND.

my code for making a call from sim908

int flag=0;
int flag2=0;
void setup() 
{
 Serial.begin(9600);
 delay(1000);
flag=sendATcommand("AT","OK",10000);
if(flag)
{
flag2=sendATcommand("ATD07354335501;","OK",10000);
}
if (flag2)
{
 delay(10000);
 sendATcommand("ATH","OK",10000);
}
}
void loop() {


}
int8_t sendATcommand(char* ATcommand, char* expected_answer, unsigned int timeout){

   uint8_t x=0,  answer=0;
   char response[100];
   unsigned long previous;

   memset(response, '\0', 100);    // Initialice the string
   
   delay(100);
   
   while( Serial.available() > 0) Serial.read();    // Clean the input buffer
   
   if (ATcommand[0] != '\0')
   {
       Serial.println(ATcommand);    // Send the AT command 
   }

Serial.print(Serial.read());
   x = 0;
   previous = millis();

   // this loop waits for the answer
   do{
       if(Serial.available() != 0){    // if there are data in the UART input buffer, reads it and checks for the asnwer
           response[x] = Serial.read();
          // Serial.print(response[x]);
           x++;
           if (strstr(response, expected_answer) != NULL)    // check if the desired answer (OK) is in the response of the module
           {
               answer = 1;
           }
       }
   }while((answer == 0) && ((millis() - previous) < timeout));    // Waits for the asnwer with time out

   return answer;
}

OUTPUT

AT
-1

I have sucessfully made call and send sms read gps NMEA data by sending command directly from computer using PuTTY software..

i have tried 2-3 convertors(232 to TTL)
since i am not using software serial i am uploading program by disconnecting module from arduino but still unsucessfull.

But i am not able to communicate it with it using arduino...

please help me finding what could be the possible mistake i am making... i am in the middle of a project but m stuck in this problem..

please help..
Thank you very much in advance....

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