Phony WordPress Registrations

I am receiving continuous notifications of new wordpress registrations (subscribers to my wordpress account). I do not know where they are coming from or how to stop them from coming, as there is no registration form available on the website (other than our contact form and newsletter sign-up forms, which each have different notification processes).

The email notifications I receive each time there is a new wordpress registrant include the following information:
– From: [email protected] (stempilot.com is my website)
– Subject: [Stempilot] New User Registration
– Body: New user registration on your site STEMPilot:Username: xxx; Email: xxx

Many of the registrants look like phony email addresses. The registrants then show up as ‘subscribers’ in my wordpress dashboard in the ‘User’ section (I have been deleting them).

Please help me figure out where/how these registrants are registering and how to stop it.

Thanks!