I had a similar problem.
Regassed (serviced) by VW in March... been running it very regularly. Worked enough for the weather at the time, albeit with a whining noise. When the hot weather started in anger (if you can call it that), the aircon refused to put out cold air, and there was funny gurgling noises from behind the dash and a whining.
It was just inspected by VW today, they found gas had all leaked out. They have regassed + UV dye... asked me to drive it around and bring it back to them in a month or when ever the air con fails. They will inspect for leaks and remedy accordingly.