<response type="standard warning">
No, you can't just cancel any service by blocking your card payments. Legally they are quite distinct actions, and depending on the situation, you may find yourself with debt collectors chasing you quite rightly for money you legally owe, damaged credit, etc.
If the service provides a reasonable means of cancelling, just use it. If it doesn't, take other action as appropriate, but don't just silently block payments without making a reasonable attempt to tell the service you are cancelling.
</response>