I had some backups in iCloud from my old iPhone. I came back to get my stuff and it was all gone. My iCloud storage was full, then when I came back it was empty and there were no backups. I DID NOT delete them. There was a lot of photos, videos, messages and contacts in there I will never get back.
Read more: https://iphoneus.org/faq/why-did-apple-delete-my-icloud-backups.html