What to do when you backup your phone, the reset, however are the reset, none of your photos show up?

I was at the apple store and one of the workers told me to upgrade my icloud storage so I would be able to backup my phone. I told him that as long as I have all my photos then he could upgrade it and back it up in order to reset it. Once I got home after the reset, I turned my phone on, signed into icloud to look for my pictures, however, none of my pictures showed up. I then went online into icloud and still nothing. Not only that I couldn't see my picture, but pictures that I deleted months ago had shown up instead. How can I restore the photos that won't show up? or if they're located somewhere else that I do not know of?