Vehicle still not 100%

My Audi A1 has gone back to Lindsay saker Audi 3 times in the past month. The particulate filter light comes on and the vehicle loses power. Sometimes the glow plug lights come on and you have to switch the car off and on for it to go off. The car also doesn't start on the turn. Sometimes you have to turn the key and hold it down and a few seconds later it actually starts to spark and start. The last incident we took the car to them last week and they said it was fine 2 days later the filer light came back on. This is an ongoing thing and we constantly have to take the car in for this. Why cant it be sorted??? if need be change the entire system as this is annoying.