Why is one text conversation not showing?

One conversation thread isn't showing at all anywhere in my hub or text messages. When I go to compose a new text and enter the contact information the conversation shows, however it seems to want to me add another participant to the conversation. I've deleted the conversation, ended the chat, deleted the contact and restarted my phone. I don't receive notifications of new messages from this contact either. I'm not tech savvy so if someone can help with simple instructions i'd be eternally grateful!!! It's a Q10.