This is very bad advice. Do not just cancel your payment and expect things to be ok. You might end up with additional late fees, increased risk scores, notices on your credit report, and collection agencies.
Cancel the service properly and always have proof.
Wouldn't just cancelling the card and sending them a email to their support email saying "I hereby give notice I have cancelledy subscription and further attempts to come will fail".
I doubt any court would go against the consumer in that situation. Especially if you never login or use the service again.
I don't know the legal details but court is a far off thing. Companies don't have to accept arbitrary notices and can send your account to collections for being past-due according to whatever terms you accepted for the subscription.
Cancel the service properly and always have proof.