How to delete a calendars

Hello,

One day, long time ago, I don't remember when, I put a calendar about french holidays on my iPhone.

Well I don't remember where I took it, but now, I want to delete it, but I don't know how!!

If I go to the calendar app, I see this (it's in french) :

I can see a calendar "Jour fériés français". I can only choose to hide or show it.

But if I go to the settings, I see this :

I can't see anything like "Jours fériés français", so I can't delete it.

I have the Calendars 5 app from Readdle. And when I look to hide or show the calendars, I see this :

I can see the calendar "Jour fériés français" like a Subscribed Calendars, but it doesn't help me to find where I can delete it.

So is there a way to delete it? Or is it a bug from iOS?

It makes the same thing with my iPad.