Let It Ride, I know a little about gambling addiction and think the casinos in question should be taken off accredited list (if they are on, I haven't checked) for this type of behaviour. I am not surprised a casino won't pay you back after you have lost at it after slipping through the net (not condoning it in any way) but to withold winnings for this reason is beyond belief! They should be wishing you well, paying out and letting you know you will never be allowed near their casino again...
You realise you have issues and can not control your gambling once started, I do not want to patronise you at all but you need to be putting up all barriers possible to stop you gambling again. Gamblers anonymous believe that if can not control your gambling the likelihood is you will never be able to, once an addict always an addict. I am not qualified enough to advise whether this is correct or not but, if so, setting time limits and signing declarations saying you no longer have a problem is not good enough - GET AWAY FROM THE CASINOS AND STAY AWAY.
I would also suggest that you get Gamblock (
www.gamblock.com , I have no connection and apologies for posting link if this is against forum rules but feel it is worthwhile for this thread) installed on each computer that you use for your gaming. However it is linked to individual computers so keep away from internet cafes and reinstall it on a new PC if you get one! Gamblock should stop you getting access to any of these sites for the period of your subscription ($75 for 1 year) so take out the longest one you can (up to 3 years I believe). The price is maybe high for the software involved but should pay for itself many times over and save you a lot of temptation.
I wish you well in your quest to come through this whichever manner you decide to tackle your addiction.