I hope not viewing the message will stop this thing. I treat unknown texts the same as SPAM in email. Only way I've been able to stop most of them is to create a Contact with a almost any name but with the number that is displayed in the list of texts. You can then go to the Phone prefs and scroll to the absolute end of you list of blocked numbers and select the "Block Contact" item. You then are taken to your Contacts where you can find the newly added spam contact. Make sure that is the one you want to block and click it,
there is NO confirmation opportunity. You will now be returned to the blocked list showing the just added blocked contact. At that point, you can scroll down and use the newly added blocked contact. Fortunately, there is an "Edit" button now, and you can correct a mistaken block by using the edit function and touching the
dot to
UNblock that contact.
It's is not as convenient as when blocking a phone call.
