Sorry this is happening. You have done your best to keep your life separate from them - for one reason and one reason only...to ensure you are able to continue to have a relationship with them. Now they do this? It hurts, it hurts bad. What should you do about it? What can you do about it? The reality is there is not a damn thing you can do about it.
Should you respond to them? To what end? Will it make you feel better? Most likely not. Make them tell you in person so you can both look into each other's eyes and see the hurt? Again to what end?
They are not going to change their minds. The decision is rendered - you are shunned and that's final. Leave it as it is.
Go about your life, and live it the way you want to.
Forgive them - for they know not what they do.