Why am I getting constant Password popups in Safari?

I made the mistake of adding one password to Safari, and now every 10 minutes there's a pop up on my screen. I tried deleting the password, deleting the app Passwords (can't), changing the settings on the app, nothing works. We don't even need this app anyway.

How can I make this go away? It's intrusive, interruptive, and just plain annoying.

[Re-Titled by Moderator]