One of the ways to prevent unauthorized charges is to use a virtual credit card. Many credit cards provide a way to create virtual credit card based on your real credit card, for example, Citibank [1] and Capital One [2]. Then if the merchant makes it hard for you to cancel, just delete your virtual credit card.

You can specify any expiration date for the virtual card (with at least 1 month validity). You can also set per-transaction limits on this credit card, which ensures the merchant can't charge more than the agreed amount.

[1] https://www.cardbenefits.citi.com/Products/Virtual-Account-N...

[2] https://www.capitalone.com/learn-grow/money-management/what-...