I try to cancel subscriptions immidiately after signing up when i only want the service for a limited time.
For an Italian newspaper's online subscription, after contacting them for cancellation via web form, my family was informed: you have to call a number and that cancellations will only be accepted 1 day before the end of the subscription.
Let me re-state that: you have to remember, one year after signing up, to call that number within a 24 hour window (maybe less, depending on their office hours), reach somebody, and hope for their honesty in confirming the cancellation, because your have no proof that you did so. Or you are locked in for another year.
Luckily, I had used PayPal as subscription payment method, wich has a separate web interface for cancellation. And also remembered the call after one year, for good measure.
But what a disrespect for consumers! Quite surprised this was apparently legal in Italy (we don't live there, it was an educational subscription).