Unable to delete photos from my Iphone!

I tried everything to 'empty' out my photos in my phones but it just wouldn't let me delete the photos at all! To be specific, I selected everything, then I delete. Next thing I know, the photos are still in the album.

Things I've tried;

• Unsync photos from iCloud, restart, proceed to delete photos
• Signed out of iCloud, restart, proceed to delete photos
• Download 3rd party software 'EaseUS Mobimover' which says couldn't delete photos due to software limitations

I mean - this is apple we're talking about.

What does such a simple task such as 'deleting all photos' seems so complicated :(