Thank you for your support, genenco.
What the casino refers to are terms that were on the bonus coupon in the lobby. They claim that it says that I can't withdraw more than $300. I read those terms carefully, posted a partial screenshot in my OP, and there are no terms saying that.
Here is a screen shot of the the wording on the first deposit bonus as it appears in the lobby:
The important term here is apparently "you may not receive more than $500 in real money. Excess bonus money will be void after conversion" (on my bonus this is $300 obviously).
Is it reasonable to interpret those words as "you may not withdraw more than $300"?
Nowhere does it say in any detail how this "bonus system" works. How is your balance separated into bonus and real money balance. As in do you wager bonus or deposit first, what happens when you wager and win off either balance, how is your bonus "converted" etc etc. A bonus that is such so huge no-win for the player, has got to be explained in some detail. This is just a huge trap. Beyond rogue.
I actually don't believe that this is how the bonus system is meant to work, it's just and excuse from a casino that can't afford to, or don't want to pay winners. If the bonus system was meant to work like that, why did they not inform me of this in any of the many email exchanges I've had over the last month and a half about my missing $5k?