The mentioned transaction is called
`Inah Bay` (selling and delivering something to another person in installments but repurchasing it with less immediate cash), which is considered unlawful in the Sunnah. Accordingly, it is an invalid transaction. The price is unlawful for them to take, the car is rightfully yours and it is up to you to give it back to them while being defective or sell it to someone else. If you have any disputes you should resort to the court for settlement and the court should settle everything, Allah willing.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.