Seat Leon Reference 1.9 TDI

I swapped my Vauxhall Astra 1.8 SRI for a Seat Leon 1.9 TDI Reference in 2009 as my family and I where going to Germany and I needed an economical car. A month later, while in Germany the engine management light came on, I took it to Seat when we got back and they fixed the problem. A week later the Service dpt called me up and asked me to come back in, as they had a part from my car they had forgotten to put back on. Since then, every few months my car will stall, jerking the driver and passenger, on motorways or back streets, its fine for weeks then just stops! then it wont start, the starter grinds and it wont work! 5 times later, seat have replaced the clutch, starter, dual mass flywheel and a few pipes, but then the other day, it cut out and wouldnt start at all, all attempts to start it resulted in the engine belowing out smoke and sparks from the engine bay. Service manager blames a dodgy starter, but its had 5 new ones! How can they have replaced them 5 times with fault ones? Never reccommend to anyone!