My anti pollutant filter light kept coming on every week when I bought the car 3 yrs ago ! Garage said it had been serviced and this is quite normal ! Anyway after 3 months changed the oil to a good quality oil to correct spec and dpf light hardly comes on at all ! I suspect that either they didn't change the oil or probably put in some cheap oil not to spec ! I also think running the car on a good quality diesel helps ( not super market fuel ) I remember seeing clouds of smoke coming out of the back of the car when it's doing a regen ! Can look quite alarming ! But of course it's putting a lot of extra diesel into the engine to clear the filter , I think this extra diesel can get into the oil putting the oil level up and contaminating it ! I suppose this could lead to the oil needs changing warning coming on !