Hugs, KI. I know the feeling. I used to get myself in a tizzy just seeing a phone number with the same area code as my XAH on my caller ID. It is a fight or flight response causing your anxiety at this point. I remember it felt like an attack against my paper-thin defense of my peaceful controlled world. It was a reminder of how vulnerable i really felt. Breathing deeply, and reminding myself that I was safe, was the best way I found to combat that response. The feeling is temporary, though intense. It will get easier with time (I know that's not very satisfying right now, but it is true).
I would suggest that, in the future, there is no need for you to respond to anyone that you don't want in your life. If you wanted to respond, you could take action to prevent them from contacting you again (as in block their number, email, Facebook, etc). Most people will get the idea pretty quickly when they are being ignored. It isn't unreasonable to ignore rude people. Give yourself permission to choose who you interact with, and you don't necessarily need to be nice about it. This is particularly difficult for most of us (codependents) to stomach.
wishing you peace tonight,
Fathom