I had a similar issue with my Mk7 2013 GTD. 6 weeks after the warranty had expired my media system just stopped functioning. The tech at my dealership did everything he could, but couldn’t get it working. VW themselves were incredibly unhelpful and I was quoted £3500 for a new head unit. Luckily for me, the dealership felt this was ridiculous and replaced it for me, I don’t know if they got anything back from VW, but they kept my custom. Whilst I’m no expert, I would have thought that the sale of goods act may assist. Is it reasonable to expect a £5000 media system to pack up after 5 years? I think not. Good luck with your endeavours.