Shuffle has an active ANN thread and a running campaign here; they are active, which means you will definitely get an explanation of why your account is being flagged.
OP stated the reason already that he was told that he is using more than one account to access the gambling site. That could have been known through IP address that the user is using.
3.4. You are permitted to have only one Shuffle Account. If you attempt to open more than one Shuffle Account, any and all such accounts may be blocked, suspended or closed, and any sums credited to those accounts will be frozen and may be deducted. If you realise that you have opened more than one registered Shuffle Account you must notify us immediately by email at support@shuffle.com.