> This is a customer service. A written notice of termination works for any consumer contract.

Not entirely. Most places don't accept cancellations over email, or require certified mail for cancellations, which just means now you have to go to the post office between 9-5.

> Unpay for it. This is the utility of credit cards.

Most places have segments in their contract that state if you do a chargeback or block a payment, they will terminate your account, and payment providers can block that card from being used on their service in the future.