How to control an led from Thingspeak server using SIM900A and Arduino?

I am trying to control a LED from Thingspeak server by using the GSM module. The data received is successfully being printed on serial monitor(which is '1' as last updated) but when I am trying to assign that data to a variable so as to control the inbuilt LED of Arduino, nothing happens.

#include <SoftwareSerial.h>
SoftwareSerial SIM900A(10, 11);
void setup()
{
  pinMode(LED_BUILTIN, OUTPUT);
  SIM900A.begin(9600);
  Serial.begin(9600);
  while (!Serial)
    ;
  Serial.println("Arduino is ready");
  SIM900A.begin(9600);
  Serial.println("SIM900A started at 9600");
  delay(1000);
  Serial.println("Setup Complete");
}

void loop()
{
  SIM900A.println("AT");
  delay(1000);
  ShowSerialData();

  SIM900A.println("AT+CIPSHUT");
  delay(2000);
  ShowSerialData();

  SIM900A.println("AT+CIPMUX=0");
  delay(2000);
  ShowSerialData();

  SIM900A.println("AT+CGATT=1");
  delay(5000);

  SIM900A.println("AT+CSTT=\"INTERNET\",\"\",\"\"");
  delay(4000);

  SIM900A.println("AT+CIICR");
  delay(3000);
  ShowSerialData();

  SIM900A.println("AT+CIFSR");
  delay(5000);
  ShowSerialData();

  SIM900A.println("AT+CIPSTART=\"TCP\",\"184.106.153.149\",\"80\"");
  delay(4000);
  ShowSerialData();

  SIM900A.println("AT+CIPSEND");
  delay(4000);

  SIM900A.print("GET /channels/798173/fields/1/last");
  SIM900A.print("\r\n\x1A");
  ShowSerialData();

  char led = SIM900A.read();
  Serial.print(led);

  if (led == '1')
  {
    digitalWrite(LED_BUILTIN, HIGH);
  }

  else if (led == '0')
  {
    digitalWrite(LED_BUILTIN, LOW);
  }

  delay(8000);
}

void ShowSerialData()
{
  while (SIM900A.available() != 0)
    Serial.print(char(SIM900A.read()));
}

Last portion of the output from the serial monitor:

CONNECT OK
AT+CIPSEND

> ⸮GET /channels/798173/fields/1/last

SEND OK
1

Solution

As pointed out by @Saurabh P Bhandari, you cannot read the same data from the serial twice, thus you'd need to read the data in a variable in the first place if you wish to use it.

String getSerialData(){
      String buffer="";
      while (SIM900A.available() ){
        char c = SIM900A.read();
        buffer+=c;    
      }
      return buffer;
     }

Then you can use String led = getSerialData() to populate led with the buffer.
Here, you need to beware that the function getSerialData would return anything present on the buffer and would look something like:

GET /channels/798173/fields/1/last
SEND

HTTP RESPONSE

It appears that you're only interested in HTTP RESPONSE, thus you can update your conditionals to be

if(led.endsWith("1"))
...
else if(led.endsWith("0"))