Call Customer Service Rationally. This is the best course of action, and it's even ideal if the casino in consideration offers live chat. This will provide you with an immediate reason for why your account was restricted, as well as an easy and effective way to unlock it.
Signing up for their player's clubs will get you some free stuff, even if you never play any of the table games or their slots. That's the most free stuff you'll ever get from any casino, beyond that it's going to cost you.