porn text messages

Got an explicit text message from these people today.  I had never called them or subscribed to any kind of service.  The message ended with the instruction to text 'stop' to unsubscribe, so I did that.

I've gotten two explicite text messages from this # and my phone and # are new. So it must be recycled. I am trying to figure out to get them to go away. I don't want to text back incase it gets worse.