cant remove duplicate entries from lists

I agree that more sort options would be helpful within list Edit.

Meanwhile, you could export your list and sort it in a spreadsheet. You could use some spreadsheet logic to identify the duplicates, and it would show the list position numbers to help you locate them in Edit.

Tedious, but doable.

There is a quick way to do this if you have seen all the movies and rated them on IMDb. Say Double Indemnity is on your list twice, if you go to the list and use the "Refine" function to restrict it to only movies you haven't seen, it will come up as unseen (strangely enough). Click "Refine", then "You and this List" and then "Titles I didn't rate" and it gives you a list of your double counts. I've used this before to solve the same problem myself. 

Only works if it's a list of movies where you have seen them all, i.e. you're publishing your favourites list. But very quick if you have.