How to mass delete spam texts from iCloud on MacBook?

On an iPhone it is easy enough to delete all text messages from unknown senders. But on a MacBook it must be done one by one. So my iCloud is full of spam texts I never asked for. Apple wants me to buy more storage. I want Apple to allow me to delete all my unknown senders text at once. Also if you turn off back up msgs to iCloud and try to deal with it later, your texts will fail to deliver. I don't understand why but it's surely a pain to deal with.

[Re-Titled by Moderator]

Original Title: iCloud Full of Spam