Constant Contact keeps unsubscribing new customers

I am so frustrated. My new customers keep getting their emails unsubscribed. They are not doing this themselves. They belong to my membership groups and need the info I am sending them. When they do not receive this info it causes chaos for all of us. I am sick of sending them emails to resubscribe. I am at my wits end. I use Shopify with Constant Contact. Is any one else having this issue?