USSD Return OK instead of Response

Question

I am working on this ussd project that would just check the balance on a modem and print it out. Howeover, I am stuck to this point where I get "OK" printed to my screen. My ussd command returns only "OK" not the actual ussd response.

I am working pyserial. So Assuming I send *124# which is to check balance, I expect the balance but it ends up returning "OK"

what is wrong.

import glob
import time
import serial
from pdu import pdu_to_text, text_to_pdu


def list_ports():
    ports = glob.glob('/dev/ttyUSB*')
    for val, port in enumerate(ports):
        print(val, port)
    print('-----------------------')
    port = int(input('your desired port: '))
    print('You selected' + ports[port])
    return ports[port]


def command_maker():
    command = raw_input('enter ATCommand: ')
    return bytes(command.encode('utf-8'))

def ussd_maker():
    # return '1' is specified here to allow return of a casted string
    ussd_code = convert_text2pdu(raw_input('Input the USSD code: '))
    ussd_command = "at+cusd=1, " + str(ussd_code) + ', 15\r\n'
    print(ussd_command)
    return bytes(ussd_command.encode('utf8'))


def convert_pdu2text(pdu_encoded_data):
    """
    Convert pdu encoded data to text(string *utf-8*)
    """
    pdu_decoded_to_text = pdu_to_text(pdu_encoded_data)
    return pdu_decoded_to_text


def convert_text2pdu(unicode_string):
    """
    Convert text to pdu format to work with gsm modems and any other
    device that support pdu data format
    """
    text_encoded_to_pdu = text_to_pdu(unicode_string)
    return text_encoded_to_pdu


def app_run(port, atcmd):
    ser = serial.Serial()
    ser.port = (port)
    try:
        ser.open()
        time.sleep(0.5)
        ser.write(bytes(atcmd) + b'\r\n')
        out = b''
        time.sleep(3)
        while ser.inWaiting() > 0:
            out += ser.read(1)
        if out != '':
            print("------response--------\n" + out.decode("utf-8"))
        ser.close()
    except Exception as e:
        raise e


def app():
    select_option = raw_input('Select your desired option. \n1. Send raw AT command \n2. Send USSD code: \n')
    print(select_option)
    ls_ports = list_ports()

    if select_option == '1':
        cmd_maker = command_maker()
        app_run(ls_ports, cmd_maker)
    elif select_option == '2':
        ussd = ussd_maker()
        app_run(ls_ports, ussd)
    else:
        app()


if __name__ == "__main__":
    app()