Can't erase old text message

[AC Question]

I have a galaxy on5, I erased a text message but it stays on my phone. I try to clear it and it comes back in like 5 seconds. My messages shows I have 1 message when I don't because of this old message I can't get off my phone. When I click on the message to reply it says to add a person to send the new message too. But I can only access the old message on the drop down from the top. Not the message widget.