iMessage / SMS not sending to one contact

I’ve had trouble within the past four hours with text messaging one certain contact. Everyone else is fine. They have been able to message me and see that I am replying with the three dots, but nothing goes through on my end. This is extremely frustrating. I took a carrier update and my ios is up to date as well. Everything was refreshed too. I try to call their phone and it goes straight to voicemail, but i can call them with a different number. Help?