Deleting Contacts Constantly

It would be great if there was an auto-delete feature for contacts. I don't need any contacts in Manychat, I use it for the autoresponder and yet I get charged based on contact number, and I only need exactly zero contacts.  I have to log in every few days to delete all my contacts in order to stay under 3,000 contacts and that is a real hassle.  Is there any way to work around this?