iMessage won't work with one contact
I have an iPhone 6 with completely updated software (9.2.1) and my iMessage will not work with just one contact. I have tried every fix I've been able to find online including logging out of my apple id, resetting my imessage, restarting my phone, resetting the network settings, but nothing seems to work. The text messages it's sending in iMessage's place aren't even being received. Does anyone know how I remedy this?
iPhone 6, iOS 9.2.1