Garage dispute

have been to garage who quoted €2900 for initial work same completed. Received 2nd call to say the car needs another €1300 of work. Same completed. Took car home. 2 days later engine light on and not idling. Garage says needs €4900 of work. Car is 171 mini. The initial work was wiring harness, cooling hose, gasket, throttle and oxygen sensor. Now they r saying needs DDE and intake manifold. Obviously from the start if I had known it would cost over €8000 I would not have done any work. Where do I stand? Any advice appreciated.