Carefree package

In May we have concluded a contract carefree package with fixed price, now the car is standing since this day in the workshop, fixed price can no longer be kept – because a new damage came to it – become significantly more expensive, the communication leaves much to be desired, since over 14 days again nothing heard. What can one do against such unbelievable people, sometimes I have the feeling the car is no longer available. Who can help?