I experienced exactly the same problem on my GTI a few days ago. I tried to adjust the ac temperature settings and absolutely nothing would change. I even tried doing a soft reset on the Infotainment system but that didn't help at all, so I switched off the ignition, left the car for a couple of minutes and, when I restarted it, everything seemed fine.
I immediately emailed my local VW dealer's and told them and they suggested that I bring the car in today for a diagnostic check, while I waited. After about 15 mins, the Service Manager came over and told me that the car needed a software update and, if I was happy to hang on for another hour, they would do it there and then. So, I drove in today with software version 1788 and I now have the brand, spanking new 1803 version. That's great service!
Let's hope it does the trick!