on this page in the screenshot, wait for a dozen or so seconds till next backup size has a size displayed & not 0 bytes & the spinning icon goes away, then & only then will or should it let u delete the backup, then turn on backup again & it should make a new backup
this works for me every time icloud gets the issue of not backing up or not deleting backups, including in all the ios 9 betas when icloud was having problems