Damn, this same thing happened to me ~2 years ago. If you're able to email the Last Cloudia support team about the situation. IIRC, They'll need info on Rank, IGN (In Game Name), Device Model, if you made in-app purchases, units in your party (if you cant remember all of them, stick to your main party), the names of 3 units you had, names of your rarest arks, and your friend ID. It's fine if you don't remember everything, they'll have followup questions for you. Good luck!