If you contact chat they can clear them down. Only necessary if you have a device that someone else is using without your permission.
In which case it would be advisable to change the login password also.
Yes indeed. And also set a Payment PIN.
You can actually blow unwanted users away yourself, as an option while changing your password; but it blows all your wanted users away too, so you have to reset them. And while it neutralises the unwanted user, his device entry remains until it rolls off the bottom as you use other devices, so there is much to be said for having the Live Chat people do it for you,