I take it you have changed the name of the (copied) qext file as well?? The qext file needs to have the same filename (before the ".qext") as the js file and be in the same directory.
If that is OK you might have a caching problem, specially in Qlik Sense desktop, which caches a lot. Try opening the app in the browser and turning caching off. I have written a small document about how to debug your extension (Troubleshooting your extension), which might help you.
Hope this helps
Thanks a lot for the response.
Actually I haven't changed the name of .qext file. But inside the .qext file name of the extension object will be mentioned I have changed that name to a new name so that both the extension objects will be different. And I deployed both extension objects on server but the new one is getting effected by old one.