I know this is an old post but our touch screen stopped working on the right hand side recently. Contacted VW who will only replace the entire unit upwards of £2500.
From the number of people with the same issue it looks like a common problem that VW (yet again) are refusing to acknowledge.
Found a local audio specialist who will replace just the touch screen. It was a fraction of the cost of VW and he said that VW always get him to replace the faulty screens of cars brought in a trade-ins but VW will not offer the service direct to customers as the whole unit makes them more profit.