Deleting photos from iCloud & all devices

I am trying to reduce my storage on iCloud by removing photos. I select the photos I do not want, delete them, then delete all. The problem is that my iCloud storage is still too high to do any backups, yet I've deleted 1500 photos! It seems that they return again when I go & check. This is so annoying not to mention time consuming. Can someone tell me please what I am doing wrong? I DO NOT want to pay $4.99 per month for iCloud as I am already paying $1.99 per month which is about all I want to pay. There are many photos I simply to not want, but I do not want to spend more hours deleting photos if they are going to return soon after.....TIA