I asked as you could have been referring to a Mac or iPad. Either can also sync images to your iCloud account. But yes, since you referenced Android, an iPhone was the most likely device.
Per muguy (and Apple does not explain this well at all) iCloud is not a backup service. It's a syncing service. You can see all of the photos you've taken with your phone on all of your Apple devices that are logged into the same user account, which makes it look like a backup.
But!, again it's NOT a backup. If the user deletes anything on their device, or on iCloud from a logged in device, it is synced back in either direction and to all other devices, where the photo(s) are deleted there, too. It's what syncing does and is supposed to do.
So, I'm strictly guessing here, but you probably needed room on your phone in order to take more pictures, so deleted what you had on the phone. Unfortunately, iCloud did what it's designed to do and synced that action to the copies in your iCloud account. This removed them from iCloud to match/sync the phone. They are now nowhere.
You could try logging into your Apple account from any other device via a web browser (and it can be a PC), just to see if maybe the photos will still be available. It can't hurt to try, but I wouldn't count on it.