Hi Adycakes,
Similar situation happened to me.. I bought my MK6 GTi back in April from a VW dealer, as it was cold I never really had to use it in April.. But obviously with all this recent hot weather, I wanted to use it. So after trying it out, it wasn't really working and after ten or so minutes (on a hot day), windows closed with the black leather, I may as well have been in a sauna.
I was quite annoyed as VW were supposed to have sold the car with everything fully functioning (was quite annoyed at myself for not checking it on pick up actually, school boy error!).
So yeah, long story cut short, booked it in at VW under warranty for an inspection as I said "possible compressor problem", along with a couple of other problems (different story!).
They carried out of a full air con service free of charge and now its as cold as ice, working perfectly.
If they try charging you, tell them to jog on!
Hope this helps. GTIOxford.