Fiat Palio Multijet Sdx — defective /irrepairable car

ihave purchased fait palio multijet diesel car sde model, dec 2008, from manickbag automobile at hubli, karnataka, vehicle has covered 11500 kms, 3tyres completly worn out, the vehicle has visted atleast 10 times to the showroom with the same complaint, the dealer is just unable to trace the fault, they try convincing but are unable to detect the fault, the vehicle wobbles b etweem 30-50 km speed .vehicle no ka 29-4383, bagalkot karnataka