I am getting spam texts that are coming in with a white (no color) bubble.

I get these every day and turning on filter for unknown senders doesn't work on them. They all seemed to be from the same place but they have multiple different subject matters. Some inappropriate. Also, they come in different phone numbers each time so I can't block the number. I have sent the spam notification (TEXT: SPAM) to AT&T many times but no change yet. Help!