You can read our guide to rejecting a vehicle here - www.honestjohn.co.uk/faq/consumer-rights/ but in brief the grounds for which you can reject a vehicle are if it is not of satisfactory quality or is not fit for purpose, which you could argue the car qualifies on both counts. You have taken the right approach by giving the dealer the opportunity to repair the issues, so if you wish to escalate and reject the vehicle we would recommend writing to the person you have been in contact with at the dealership and the dealer principal and sending the letter by Special Delivery, outlining the issues that you have experienced and explaining that you want to reject the vehicle on these grounds.