You didn't follow them on social media, did you? If you did, delete them. You can't get over them if you keep seeing what they're up to. Similarly, if you have them listed in Skype, or anything else, delete it. You don't even want to see their name, because every time you do, it will remind you of them.
You need to be very frank with yourself and say, "Listen, this person never liked me. It was and never is going to happen. Nevermind."
You need to not care. Tell yourself you don't care. Say, "Oh well. Cest la vie." If they come into your mind, shrug it off and think about something else. Do not dwell over it, or it will continue to circle around your brain, making you think "This is important." When it isn't. It doesn't matter. It's from the past. You've moved on.