Old iPhone backup in iCloud will not delete

Got a new iPhone 11 Pro to replace my iPhone 7. I have tried all the tricks I can find online to delete the old backup but to no avail. I've tried from my new phone, from my iPad and from my MacBook Air. Same error message on every device. That old backup is using about 17gb of my 200gb storage. Not terrible but I'm using Family Share and want to add my daughter so all our phones are backed up to the same place. Any new tricks?

FYI, I was able to delete the latest/newest backup of my brand new iPhone 11 Pro. But not the old backup.