Having problem sending message using gsm sim 300

Code C - [expand]
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import serial
import RPi.GPIO as GPIO      
import os, time
GPIO.setmode(GPIO.BOARD)    
port = serial.Serial("/dev/ttyAMA0", baudrate=9600, timeout=1) # Enable Serial comm..
# Transmitting AT Commands to the Modem
port.write('AT'.encode()+'\r\n'.encode())  # '\r\n' indicates the Enter key
rcv = port.read(10)
print (rcv)
time.sleep(1)
port.write('ATE0'.encode()+'\r\n'.encode())      # Disable the Echo
rcv = port.read(10)
print (rcv)
time.sleep(1)
port.write('AT+CMGF=1'.encode()+'\r\n'.encode())  #Select Message format as Txt mode 
rcv = port.read(10)
print (rcv)
time.sleep(1)
port.write('AT+CNMI=2,1,0,0,0'.encode()+'\r\n'.encode()) #New SMS Message Indications
rcv = port.read(10)
print (rcv)
time.sleep(1)
port.write('AT+CMGS="9652157636"'.encode()+'\r\n'.encode()) # Sending a message
rcv = port.read(10)
print (rcv)
time.sleep(1)
port.write('temperature is 27 C'.encode()+'\r\n'.encode())  # Message
rcv = port.read(10)
print (rcv)
port.write('message from sim 300'.encode()+'\r\n'.encode())  # Message
rcv = port.read(10)
print (rcv)
port.write("\x1A".encode()) # Enable to send SMS
for i in range(10):
    rcv = port.read(10)
    print (rcv)