If your husband is Shia, we can assume that he asked for the proper conditions of divorce to be met. It’s valid for the judge to say it as long as there are 2 just witnesses present when he said it. If he is Sunni, then the divorce is definitely valid and you are off the hook from him.
In any case, if your husband is Shia and he told you I did a valid divorce, you can take his word for that and consider yourself to be divorced from him. You do not have to investigate how the divorce happened.