Why not send a message reminding them of the service, and giving an easy one-click way of cancelling? You could include some info on how they can use your service as well of course.
Talking about Netflix specifically: if I don't log in and watch something for a week they will start spamming me with emails like: "Here's a show we think you'd like", "Continue watching show X", "New season of show Y is coming to Netflix next Tuesday".
They really seem hell-bent of making me watch something, just in case I was considering cancelling my subscription.
