Where to complain to Apple about an premium reseller that is sending spam? I have clear information that iStyle, a Premium Apple Reseller is sending commercial email messages to people who did not subscribed for that.

In addition to this, their "newsletter" contains no information regarding unsubscribing.

I want to send this complaint directly to Apple because this would be the only way that could put enough pressure on them to change their practice ASAP.
Opinion: You should take it up with the company in question first. Give them a chance to change their practises before informing the mothership.

The contact number listed on Apple’s Web site that seems best suited is the one intended for “Reseller Referral (Resellers, Trainers, Consultants)”, (800) 538-9696