how to fix a vauxhall astra 1.7 tdi mark4 ?

ive got a vauxhall astra 1.7 tdi mark4.it jerks and stalls.first i took to a garage and the mechanic changed the air flew meter,it got ok for few days then started it again.i decided to change the fuel filter on it and also cleaned the fuel filter container which it had had some robbish in it, because someone told me is a common problem on this certain model but after few hours of driving it did it again.the car has already cost me over 100 pounds.can anybody tell me what is causing it please.thanks