Need a way to delete duplicate contacts

I use an internet service provider (Cox Communications) for my email and the Windows 8 Windows Live Mail client (just upgraded from Windows XP and Outlook Express).   I have many duplicates in Contacts, spent hours deleting and when I logged back in, they had all returned.  I don't use Hotmail nor do I want to.  I actually keep my 'good' list of contacts in gmail as that seems to be the only thing I can figure out and which seems to work.   But I'd like to be able to delete the 5000 contacts in the Windows Live Mail Contact folder and start over.  Any solution to this?