It sounds like you have Adaptive Mode turned on. I'm not sure they can change their answer, they can just check it (though maybe changing it counts as a second attempt)...it could be that is Immediate Feedback that doesn't allow answer changes. I don't use adaptive and haven't for...14 years? Hated it...but a lot has changed. Interactive with multiple tries lets them check their answer and retake (possibly getting fewer point).
Anyway, if you want them to not get any feedback until after they submit, use Deferred Feedback in the quiz settings for question behavior.
