Feel Cheated and done down

Hi, i have purchased a Nissan Micra 1.2 Visia 2015 from CMH Nissan Highway and their after market service is pathetic and a don't care attitude. It's not even 6 months and my car has some rust spots and I've realized it was done up previously and sold to me. Their excuse for not assisting me is that I've taken my car to a RMI service centre to conduct a 60,000km service. The car was purchased at 56,000km. Gateway Cmh Nissan have confirmed that this car was previously done up.