Syncronizing problems

I have recently purchased new servers and have successfully migrated all users from the old server to the new server. My problem is that I cannot stop the old server from syncronizing when the user logs on or off. I have setup the users "my documents" folder to point to the new server. So the syncronizing is \\newserver\users\username and when ever this use logs on the syncronizings goes to ; \\oldserver\userss\username as well as \\newserver\users\username. The new server synconizes successfully but when it tries the old server it fails , because the server no longer exists. I need to remove the reference to the old server.