FOS (or the financial ombudsman) have a lot of teeth and from the perspective of someone who works in financial services they are generally pretty feared (and any time you go to them the firm you complain about has to pay for their fees!) - quite often a financial firm will try to resolve a complaint you have first as they don't want to have to hand you off to FOS who more often than not find in the customer's favour. So if you've bought a vehicle on finance or if the warranty is administered by VW financial services then I'd suggest that route - you need VWFS to give you a final deadlock letter before you're allowed to go there in order to show they aren't willing to go any further.