Can anyone explain why my Icloud storage is full but Icloud drive is empty? I have no other files and sync is off

I use an Ipad, I solved the problem by going to (a) settings, (b) tap "your name" at the top of the settings menu, (c) tap "Icloud" on the menu on the left, (d) tap "manage storage", (e) tap the item which contains the files to be deleted, "documents, apple books etc, (f) tap delete data, or documents and data. That cleared out my Icloud folder. I had only ebooks in Icloud which I had completely deleted online as windows explorer on my PC refused to delete any (apparently another MS snafu). My Ipad however continued to show my Icloud as almost full. I had never saved any documents, photos etc in Icloud, only ebooks, however my Ipad continued to report my Icloud folder as almost full. On following the steps above I was able to delete 4.8gb of documents which I had never put in Icloud!