Cannot delete custom cron event

Hi, I created a cron event with a cron schedule every 20 minutes. This cron should fire email notification, but it doesn’t work.

So I want do delete this cron event. I see two of them. One of them I can delete, but after refresch the page, this appears again. The other duplicate nothing happend. Even if I want do edit the cron to run it all 15 minutes, it doesn’t take this changes.

Everything is on the latest version.

What’s going on?

Can you help me?