Notifications ..

How is it that sometimes people tell me they registered , and sometimes I am not notified at all , and so evebody is stuck , as I can't activate

Go into Admin / users + groups / user settings and make sure new accounts activations are Admin and send notify email on new user registrations are also set to admin.
To activate them manually, same section but click on users and find user names, check the box to yes next to user is active, save. You will have to repeat that for all users that are not activated.