You're describing a situation where you agreed to receive email, changed your mind, and then accused the sender of spamming you for not magically adjusting his behavior to your unstated whims. This is almost the definition of unreasonable behavior.

If you genuinely did not give permission to contact you, sure, go ahead and flag as spam. If you regret giving permission (maybe because you didn't really want to give it, maybe because the communication you're getting isn't what you'd hoped, whatever), the sensible thing to do is just unsubscribe.