Imessage issues

My issue seems to stem from Imessage. I have a Iphone 5c, completely up to date. I am unable to receive imessages and normal texts from one contact. Imessage hasnt been perfect, every so often I'll send a message and this contact doesnt get it, but only for one contact. I can iMessage and text other contacts just fine. Turning imessage off and back on has helped sometimes, as well as restarting my phone. Now that has had no affect, and we havent been able to text each other since 1 pm, December 22. I have tried deleteing the contact and deleting the thread, neither of which has worked. Any solutions would be greatly appreciated.