I did bad in my a levels and I'm thinking of retaking the year
Why do you think that you need to take those levels again?
I didn't study hard enough and I want to prove my parents wrong
Retaking exams are something you thought about for a good reason. Doing poorly on exams is never a good way to do well at school, so next time make sure you concentrate on them much more with passion to get the answers right. If not then your studies will be worthless and your future won't be that good.
I'm thinking of cheating and getting someone else to buy exam papers.
You should study harder for the next time. I know that you are upset that you did not do as good as you hoped, but do not cheat on these.