AFAIK the only information they shared with you was that the payment method using was related to someone who is registered with GAMSTOP. They didn't reveal any personal information and you connected those dots yourself.
Casinos have to take self exclusion and responsible gaming very seriously. It's likely they believe that the excluded individual got you to gamble on
their behalf OR that the excluded individual signed up
impersonating you. This is a real thing that happens and there is even a player who recently posted on this forum about doing just that with his wife's identity whilst using their joint account.
The GAMSTOP element really complicates things for you. People have been able to get past joint account 3rd party accusations through providing
a lot of proof. With payment method being tainted by a GAMSTOP exclusion it somewhat ties the hands of the operator as they are bound to do several things including voiding the balance.
It is also difficult for you to actually prove you were the one gambling on the account or acting of your own volition. This really is the crux of the issue as this uncertainty makes it nigh-on impossible to give you the benefit of the doubt as they have to stick to their responsible gaming regulations and the only thing they have undeniable proof of is that the payment method is jointly owned by an excluded individual.
The account sign up, gameplay and usage is, to them, opaque. They have no way of knowing who was actually using the device or behind the decision to gamble. Even if your wife was on holiday in Australia at the time of these events, there is no way to know (or to prove for that matter) whether or not you were gambling on her behalf.
Whilst you can go through the full chain of the complaints process (internal > PAB > ADR etc), your chances are extremely low as you won't be able to irrefutably prove that your wife had no hand in the account or the decisions to gamble. There is also a rep on the forum (
@EGO ) who may chime in but it's very likely what I've said will be echoed. Their hands are well and truly tied.
I believe you are entitled to receiving the deposit back and you should take this as a very expensive lesson on why you should never play with a joint account as it just opens you up to all sorts of issues. If you want to continue gambling online, I suggest you open a separate account to do so.
It's worth mentioning that if you still reside at the address registered with your wife's GAMSTOP account, that you may run into issues with that connection in the future as well. Not only that but some operators only allow one account per household. If you now live at a different address compared to GAMSTOP and use a new bank account, you shouldn't run into any more issues.