This is a well known issue, well documented at www.honestjohn.co.uk/carbycar/ The problem came from the outside manufacturer of the chains using worn out machinery to stamp out the links of the chains. The burring this causes, coupled with VW's ridiculous 'longlife' oil change regime, leads to the failures. From around 2013, VWG EA211 1.2 TSI and 1.4 TSI engines were gradually switched to belt cam. Only the old 3-cylinder Polo engine from 2009 was chain cam, then the 4-cylinder 1.2 TSI 105 from 2010 and the 1.4 TSI 180 Twincharger. The others were belt. You're right that responsibility rests with the 'supplier' but if the link between 'supplier' and 'manufacturer' is broken, as in this case, and particularly if the car has been independently serviced, then claiming is difficult.