If you think, your Smart has a serious defect that affects the safety of the vehicle, report it to the Smart Dealer immediately. If you’re not happy with how the Smart Dealer is dealing with your report, in the UK you should contact the Driver and Vehicle Standards Agency (DVSA).
But before that, you can describe the fault of your Smart in our forum. Maybe some other Smart owner will learn that he experienced the same issue. Multiple occurrences of identical defects mean a better chance of success in a complaint filed with the DVSA. Our website is visited by Smart owners from all over the world.