I've had an ongoing electrical/computer fault in my 2008 VW Polo since 2010 when it was still under warranty. It's been taken back to the dealer five times - three by tow truck - for failing to start. Every time they hook it up to the computer they identify faults, but then it seems to reset and they tell me they can't fault it. They are now charging big money just to look at it when I'm sure it relates back to a warranty repair. Any suggestions, other than sell it?
They have been able to identify faults, and should have a record of what they are, but it would appear that there is an underlying fault that is causing the problem that they have not been able to find. Continue to press the dealer and VW and ask for direct assistance from the company to resolve this issue. Other than that I would suggest you take the car to an independent service agent that specializes in VWs, one prepared to dig deeper, and have them go over the car for you.