Promised replacement still oustanding after 3 year

We purchased a VW Tiguan for my wife which just came into stock and there was a crack in the side mirror with indicator. We were informed that it will be replaced once the part arrives. This never happened and we were subsequently informed that the part arrived but was returned to the parts department because we never enquired about it. <br> <br> Since when is it the customers responsibility to follow up.<br> <br> Every time we service the vehicle at a different dealership we get informed that the mirror must be replaced and get quoted for it. When we tell them that it was meant to be replaced they say its another branch and therefore not their responsibility.<br> <br> As a result of this I've stayed away from VW, as this is my wifes vehicle, and prefer buying my vehicles with Reeds who not only provide good value for Trade ins and but also good al round service. Because of this VW have lost out on a sale and everytime I consider buying a VW I'm put off by this experience and decide on an alternative.