I'd try to keep my head up, there's no way you should even consider giving up this early in your (academic) life. I can't begin to understand how it would feel to have poured your heart into something and work so hard yet only to find out that not only is it credible but deemed and someone elses work and you are deemed a plagiarist when you have nothing in common with one. The embarrassment would be bad enough but the 0 credit compounds it. But dont let it affect your future ventures, it may feel as though aqa are holding you back but this is one obstacle in one subject and if you push hard enough you can still hit the high grades. Believe in yourself, although it is unfair that you should be subject to this so early in your education (if at all) hence why I think you're finding it hard to get your head around it. Things will work out if you persevere, regardless of path you choose, although in this case it may to best to leave the past be and move on, getting too hung up may affect future prospects and you dont want that. Yet I can also see why you'd pursue things to try and find closure as well as see if there are any marks to be gained. It shows you still are interested in pursuing your education, even if it's elsewhere. But regardless of what you choose, I'm sure you can do it. And considering the essay that was your original post, I'm sure you didn't intend to plagiarise, but if that's how aqa see it, well like I said it's your decision