How can I recover iCloud data deleted from both iPhone and iPad?

As Servant of Cats suggests, iCloud Backup and iCloud Photos are two different things.

iCloud Backup makes copies of some things on your iPhone or iPad and saves them so that you can restore you device from scratch, like if you buy a new phone. See this:

What does iCloud back up? - Apple Support

Note that iCloud Backup only backs up things that are not otherwise copied to iCloud. So, if you also use iCloud Photos and iCloud Drive, then iCloud Backup doesn't repeat those things.

iCloud Photos is a synchronization service. When you engage iCloud Photos on a device, then the Library on that device is kept exactly the same as the iCloud Photos Library. So, for instance, if you take a picture with your iPhone, it is added to the iPhone's Photos Library, copied to iCloud Photos Library, and then copied to the Photos Library on each of the other devices that you have connected. If you delete a picture on your Mac, then that picture is deleted at iCloud and on all the other devices. 

So you can't think of iCloud Photos as a backup service, since it backs up mistakes, and there's no way to undo them. Whatever you do with Photos on your device-- it happens everywhere else.

iCloud Photos is completely separate from iCloud Backup.

If you're interested in saving storage space, you can use Optimize Storage on the Mac, on your iPhone, or on your iPad. You can set this on any device, independent of the others. If you set a device to "Optimize Storage," then Photos may store only smaller images on the device and rely on iCloud to keep the full sized images. So, if Optimize is chosen, and you want to edit or crop a picture, Photos will reach out to iCloud to get a full sized image for you to zoom in on. It's the same for zooming or printing or anything that demands the full picture. Your optimized Library may take up less than 20% of the space of a fully downloaded Library. On my iPhone, Photos takes up way less than 10% of the space it uses on my Mac. But an optimized Library may be kept larger than that if the extra storage space is not needed.

Does that make more sense?

So, is there no way to recover them?

Did you check the Recently Deleted albums on the iPhone, the iPad, and https://www.icloud.com/ ? If your photos are there, you can recover them (see Support article). (If your iPad is using iCloud Photos, you'd probably want to enable "Optimize iPad Storage" first, so it's not forced to try to store full-size copies of everything.)

Delete photos on your iPhone or iPad - Apple Support

If stuff has become permanently deleted, because you let it remain in the Recently Deleted album for too long, or because you went there and deleted it a second time, it will be gone. As the Support article explains,

"When you delete a photo or video from this album, you can't get it back."

This is why you need to be careful when deleting things.

Also why you always want to keep copies of your photos somewhere other than just on your iPhone or just on your Pad. Put all your photos in one basket – and you will lose them all if anything happens to that basket.

iCloud Photos appears to be better than the alternatives of turning iCloud Photos off and

• Including photos in automatic iCloud backups. (You should take advantage of your iPhone's ability to make automatic backups. But you can't see what is in a backup without restoring the whole thing onto a device – wiping the contents of that device in the process. You can see what's in iCloud Photos in a Web browser.)
• Making automatic backups that exclude photos and videos, at a time when they aren't being saved to iCloud Photos, either. (Yes, there is a setting that lets you do this. Someone who thought it was a great idea to use that setting got burned when catastrophe happened and there were no copies of their photos available to be recovered.)
• Not making backups at all.

If you use iCloud Photos to synchronize photos to a Mac, and make local backups of the Mac, that gives you an additional way of safeguarding the photos.

Ir sounds like you are not quite clear on the difference between iCloud Photos, backing up photos as part of iCloud backups (when iCloud Photos is off), and not safeguarding your photos at all.

If they are not in the Recently Drleted album on either device, and cannot be seen in the iCloud Web interface, they are probably gone.