The google (blue icon) messaging app has spam-protection under settings so maybe try that app if you aren't using it already. Many carriers will default phone to a weak-posterior "messaging" app instead of the default/leading-edge/blue google app. Google probably picked blue for their messaging app icon because everyone knows blue is the best message color due to iMessage. On android, you can have multiple messaging apps on your phone and switch back and forth which is "default" as you see fit - you will not lose messages.
Another idea is to disable MMS messaging. Another idea is to disable group messaging. Final idea for you to consider is to disable both group & MMS. let us know how it goes ! best regards.
when they send the message in an email, there's no way to block.
i usd to send emails, as messages to my kids, because i could use a real keyboard, instead of the tiny one on the phone.
something similar to: email@example.com