Yes I understand. I dont think you would be able to reject the whole car because of this - they should fix it, even if you get a second opinion. I can not see a Court saying you are entitled to a refund 100% on the basis a small overall part is not working. This is because its not as if you cant drive the car, you can - its more of a comfort thing.
But if you are not happy you can try and demand a refund and sue them for breach of contract. But if I were you I would get a second opinion, someone else to look and fix it. If that is fixed then you would be entitled to claim that additional cost of repair. That is more realistic.
But because you have already had a number of repairs to the car, you are not entitled to a refund. If you had NOT had a repair then you could have rejected the car, but the law says because you have had 2 repairs you can't claim a refund.
I am sorry if this is not the answer you want and certainly not the one I want to give you, but I have a duty to be honest.
But you can certainly sue for breach of contract and claim loss and damage.
Can I clarify anything for you about this today please?