Yeah, all you need to do in law is notify the seller in writing within 30 days ( but the sooner the better ) that you want to return car and a full refund, try to keep it peaceful and sellers will know that in law you are fully within your rights. You only need to resort to reports and local trading standards if dealer digs in, which if they have any sense they will not, as they are on the losing side.
Try not to discuss things over the phone as there will really be no record of what was said or agreed.