Mass calls are one-time calls to a large number of subscribers. Usually, these are single calls made at a pre-selected contact base to tell potential customers about new products or services.
Automated calls are the ones that are made following some significant event in CRM. For example, if a customer left a request for delivery, the automated calls bot will receive information from CRM and call the client to clarify and confirm the information. If the information is incorrect, the bot will be able to change it in the CRM.
In a nutshell, automated calls are continuous and are stretched out in time, because they depend on CRM events, while mass calls are usually carried out once at a given contact base.