Exactly the same situation with me mate. I wish I'd done what Luke suggested before they drove off!
I just noticed that when I got back to the car, the rain sensor area was just full of air bubbles, so obviously wasn't replaced. They'd simply shoved the old one back on again, and obviously once you've broken the seal on a sticky part, it's not going to back on again the same. Useless dimwits. No one takes pride in their work anymore.
Yes, aftermarket screens are utter sh*te. At least 1-2mm thinner than OEM I would guess. How else can they crack so easily after replacement, and from a stone at 40mph? So yeah, 1 week after screen 1 was fitted, screen 2 needs replacing now too. It's all a scam to keep AutoGlass et al in business....but VW want over £500 for a screen
I looked into binning off the auto wiping and replacing it with an old school manual variable wipe, but apparently the only way to do it is to unplug the rain sensor in the mirror, then the motor control module defaults to manual adjustment.