iCloud Backups removed by Apple
iCloud Backup only stores the most recent backup of your device. Every time you take a new backup, the old one is automatically erased.

This is how it is supposed to be, and how it always has been (or at least for multiple years). It’s not something new, nor is it specific for your account. It doesn’t matter how much space you’ve bought, how much you’ve paid or how much free space you have.

You can have multiple iCloud backups stored on your account when you have multiple devices, or backups of older devices that you no longer have. As far as I recall, it is also possible to have multiple iCloud backups stored if you have done a major iOS update, so that you have the latest backup from before the upgrade, and the latest backup from after the upgrade.

There’s no user-accessible way of accessing backups that have been overwritten in this fashion. I doubt that Apple has any way to restore such backups either, as the disk blocks probably have been reused for other purposes in the mean while.

There's also no user-accessible way of asking iCloud Backup to keep two or more backups of the same device at different points in time.

If you want to have multiple point in time backups of the same device, you’ll need to use iTunes and backup on a local computer.