For 2021, you still could qualify for a Premium Tax Credit even if your income is over 400%. However, a $12,000 credit seems extremely unusual, so I suspect that something could be miscalculating.
In the event you wanted to tell me all of the numbers that are showing up on Form 8962 (or better yet, a picture of it with any of your private information removed), I would be able to tell you if it is correct or not.
