My photos won't delete. Please help iPhone 4S

I want to delete all of my photos, but every time I go to do so, after I have selected them all, I hit the delete button; a few seconds roll by, and then my screen ex's out and goes back to the main screen of my iPhone. No photos were deleted and I don't understand why not. This is my fourth refurbished iPhone and I do not want another one because on my third referbished iPhone replacement, they gave me a new battery for free because they that one was defected. I've never had any water damage or any other damage, ever. I am extremely unhappy with Apple iPhone 4S, and I do not recommend it to anyone. PLEASE HELP!