Based on my Audi, but I can't imagine things have changed that much, I had a similar issue but just affecting the upper vents. All the vents have a motor to control air flow and these can go wrong. With yours it sounds like the one that allows air to initially enter the cabin may have broken. The blower motor should be behind the glovebox so taking that out might be the first thing to do, you should be able to see some of the motors with that out. If you change the direction of flow controls, see if they adjust. Chances are most of them will except for the broken one. This is all assuming you are out of warranty of course! They should be easy enough to remove and replacements can be bought s/h. I'd suggest checking the fuse box before all that just in case one has blown. You could also remove the cabin filter and see if air is coming from the motor there. A slim chance might be leaves having got into the blower blocking the exit, when I changed the blower on a car once there was quite a lot of muck in it but it was a much older car, a MK7.5 shouldn't be that bad yet!
Oh, and if you do find a motor broken, whilst you wait for a replacement you can just manually open the vent (with the motor out of the way) to let air in. I fixed mine for about £15 and it was fairly easy.
