In the first instance you should ask the casino to explain the decision to refuse payment. Keep a record of all correspondence and be polite. In many cases players have misunderstood the terms around wagering bonuses and the situation is quick to be resolved. If you are not satisfied with the explanations and still believe they are withholding monies without good reason, try to escalate your concerns to a manager. Be patient. Let them investigate and come back to you. If they don't respond to your concerns in a reasonable amount of time, and you still believe the casino is holding your payout in breach of regulations you can then proceed to file a formal complaint. This must be directed to the regulator who issued their licence. The regulator will then investigate thoroughly and arbitrate.