Whatever you do, do not contact them or allow them to contact you. They need to realize that they are dead to you and not even worth being told that by you directly. They need to figure out on their own that any value they ever had to you was thrown out the second they did what they did, and they need to be in a position to psychologically punish themselves for it for a long time before they are ever given even a chance to earn back contact.
I do not receive notifications, so using the @ feature will not do anything. I might see your post and respond though if I have already been in the topic.