telegram bot – Chat not found

I am totally new to telegram_bot. I want to execute a bot.send_message() in the following code (as commented in the code), but can’t do so. Please help.

!pip install python-telegram-bot --upgrade
import telegram
bot = telegram.Bot(token='**************')
bot.send_message(chat_id='******', text="I'm sorry Dave I'm afraid I can't do that.")

It errors out as :

1 bot.send_message('mardepbot',"I'm sorry Dave I'm afraid I can't do that.")

/usr/local/lib/python3.6/dist-packages/telegram/bot.py in decorator(self, *args, **kwargs)
     63     def decorator(self, *args, **kwargs):
     64         logger.debug('Entering: %s', func.__name__)
---> 65         result = func(self, *args, **kwargs)
     66         logger.debug(result)
     67         logger.debug('Exiting: %s', func.__name__)

/usr/local/lib/python3.6/dist-packages/telegram/bot.py in decorator(self, *args, **kwargs)
     88                 data['reply_markup'] = reply_markup
     89 
---> 90         result = self._request.post(url, data, timeout=kwargs.get('timeout'))
     91 
     92         if result is True:

/usr/local/lib/python3.6/dist-packages/telegram/utils/request.py in post(self, url, data, timeout)
    307             result = self._request_wrapper('POST', url,
    308                                            body=json.dumps(data).encode('utf-8'),
--> 309                                            headers={'Content-Type': 'application/json'})
    310 
    311         return self._parse(result)

/usr/local/lib/python3.6/dist-packages/telegram/utils/request.py in _request_wrapper(self, *args, **kwargs)
    221             raise Unauthorized(message)
    222         elif resp.status == 400:
--> 223             raise BadRequest(message)
    224         elif resp.status == 404:
    225             raise InvalidToken()

BadRequest: Chat not found