I have a prepaid service through straight talk, but I don't have at&t service at all. Only thing is my sim card is at&t and my service bounces off of their towers. So I don't understand why I am getting this message on my Samsung S5 active. My Samsung Galaxy Note 3 was the only phone on an at&t plan but with a completely different phone number. So why would I get a message for it? It doesn't even say how to use it, or where to enter it in at.