Trapunto review for Mailchimp Email SMS Marketing

ShopSync seems to do an excellent job until we passed the 2,000 limit on MailChimp. I cleaned our contacts of people who haven't been engaging, and our subscriber count became accurate again, freeing up room. However, looking today, I somehow gained another 20 or so contacts and seeing they aren't subscribed, I cleaned the list again. It seems like whoever is making a purchase is automatically being added to our contact list. Is there any way to not allow that to happen? I really don't have time to maintain my contact list daily.