Photos not backing up to icloud

About two months ago I purchased extra GB storage for my cloud ( the cheapest option) so I could download my photos for more space. After trying and trying again my photos wouldn't download so I took the phone into apple where they told me I needed to purchase more GB in order for all my photos to download which I did. Now paying for the 200GB icloud storage and my photos still wont download. I am at a loss for what to do. Anytime I go to back up my phone, it will back up everything else BUT the photos. I have about 48GB of photos so whats the problem? Why wont it go