mohsinffaiz What is the "this" that you have done - this thread talks about a whole bunch of things? You need to be more specific if you want some help.
What port forwarding rules do you have in place? Are you using Dynamic DNS? What exactly changed between when it was working and when it wasn't? How are you trying to access TVHeadend remotely? e.g. the web interface, playing channels via some sort of client - if so what client? Have you reconfigured your client(s) since the external address change?
Without more information there's simply no way to help you I'm afraid.
