Look my friend, you should have disconnected the internet connection before you vacate that house. That internet connection is still in your name and QTEL is not responsible if someone else is using your internet connection. I think it will be better to settle it with the family who has taken over the flat and used your internet connection. As far as the Internet is in your name QTEL will ofcourse take action against you if the dues are not settled. Act before it will get too late.