From the comments, Oracle told them to enable encryption to solve a problem with backups. They did, and they kept the master key to the Oracle wallet. The Oracle wallet is read only, they could never put something in it or fail to put something in it. The encryption system could and should have put encryption keys in it, but didn't.

That's the Oracle failure. "Enabling Oracle encryption according to their instructions, failed to do what it should, and we lost access to all our servers and all our backups because of it".

There's also a separate failure of administration on the client side of not practising working with encryption before using it in production, and not testing recovery and noticing the wallet was empty and the backups were unusable before it became a disaster, but the fact that it did become a disaster is a failure of Oracle's system.