Ah, bummer. I knew as I was posting that you no doubt had looked around thoroughly for those settings already.
The only thing I can think of at this point is to try a 3rd party SMS/Text app that allows you to block text messages -OR- an SMS/Text Blocking app that you can use with your existing Messages app (there should be several available of each type in the Play Store).
3rd party SMS/Text apps are easier to install and use than a few years ago, thanks to later versions of Android that allow you to specify which installed SMS/Text app you would like to be your 'main' app (instead of disable this, enable that, clear this, and jump through hoops to find conflicts, etc.).