Sounds like you issue isn't lack of heat, but moisture in the car. Soon as you shut down the cold windshield next to the hot engine bay causes that condensation.
Check for any water under floor mats, or in the hatch, water tight seals and MK7 are not two words that are commonly spoke in the same sentence.
Oil Hammer is correct ambient air in winter is crazy dry, so that moisture that's in your car has been there for quite some time. Try and drive the car get her nice a hot crank the cabin heat, and then crack a window or two, get some dry air into the cabin and dry it out. Another option is get some of those silica gel packs and toss under a seat.
Also don't feel bad it seems like it may be a GSW wide fault.
https://forums.vwvortex.com/showthread.php?9264959-Water-Infiltration-issue-Non-Pano-Roof