Does the casino already know about this? If not then tell them and ask for refund of your deposits. Btw how much is in your account as of now? 

I registered an account with 22bet recently and deposited several times and then  it was closed as I had a self exclusion already in place which I had obviously forgotten about. I used same name DOB phone number address etc so I don't understand how the casino didn't flag the duplicate account immediately. I understand any winnings won't be paid but surely any deposits should be refunded?? Does anyone know whether I have a good case

Yes, there are several ways to determine if an online casino is legitimate. The most important factor is licensing; a casino with a license from a recognized authority, such as the Swedish Spelinspektionen, Malta Gaming Authority, or UK Gambling Commission, is generally considered safe. You can usually view the license information on the casino’s website, which is public and accessible to users. Other criteria include secure payment methods, fair and audited games, transparent terms and conditions, and positive user reviews. For an overview of casinos that meet these standards and to compare features like bonuses and perks, resources like askgamblers.com or casinor.com can be helpful for research before choosing where to play.

I've never heard of this casino, and even searching the Net I couldn't find anything about it.

In general, at most online casinos, when a withdrawal request exceeds a significant amount, the casino must conduct a thorough check to verify that the player has complied with the casino's terms and conditions, and especially the bonus conditions.