How to report competing app which has bypassed In-App-Purchase and started using third party payment processor
Apple's App Store Review Guidelines changed in September last year, specifically regarding these types of apps, known as &quot;reader apps&quot;. It might be that your app that was rejected earlier might be approved today.
I don't think Apple has any official contact for complaining about competitors. You have no proof that they are in violation of anything, as your competitor might have a special agreement with Apple that you know nothing of.
I would try submitting your app for approval again and see if you can pass the test this time around.