Mailchimp Email SMS Marketing

I've been using MailChimp and the ShopSync app which MailChimp now bought. Having problems with high abuse complaints, although I have no idea how that is possible since we are a small company that follows all the strict guidelines. Then for some reason customers are not syncing correctly. People who have unsubscribed can't resubscribe. It's a mess. However, the customer service is helpful if you have a paid plan and they are helping me sort it out, which is nice to know they are reliable in that sense.