Unable to delete contacts created on an Altice Android phone.

Hello,

I bought a low-end backup mobile phone at a tobacco shop. It's an Android phone from the Altice brand.
I want to delete contacts created on this phone, but I can't do it; it says:
"contacts from your read-only accounts cannot be deleted, but they can be hidden."
Unable to delete, is this serious, doctor?
I want to clarify that these are indeed contacts created directly on the phone.

It's really strange...
Thank you for your help.