HELP 2009 Q7 3.0TDI Swarf in fuel system dont start!

[ali0009]

Hi guys, im new to this. i have a 2009 q7 its still under warranty and has covered 37,000miles. last week it broke down, completely shut down after a week at the dealers today i was told by Chingford Audi that they found metal fragments in the fuel system i:E filters, fuel pump etc and they are claiming its due to dodgy fuel or petrol being used previous by mistake! ive owned this car since new and have always had is run proper and always serviced by AUDI. they are refusing to do the work under warranty? on what grounds can they just say its my fault when the tank has diesel in it and NOT petrol?

HELPPPPPP.

Thanks.