People are signing up while my site is in coming soon mode

Not any more. While your page covers the whole site, nobody can make a new account: WordPress's registration form sends them back to the sign-in form, which says the site is not open yet, the Register link is gone, and WooCommerce's My account page and checkout refuse new accounts too (a shop that sells to guests simply stops offering one, and the order goes through). Before this, with Anyone can register ticked under Settings → General, the registration form stayed open whatever the mode said, and bots found it.

Signing in, resetting a password, and everybody you let in on the Access screen are not affected. If you do want sign-ups before you open, tick Access → New Accounts → Allow new accounts while your page is up. Nothing is refused while your page covers only part of the site, or in Shop closed for orders.

Accounts made before you updated are still there. Check Users (with WooCommerce, Customers shows when each one signed up) and delete the ones you do not recognise.