VW (and others such as some Jeep) uses an electronic parking brake which requires a scan tool to command the ECU to enter maintenance mode in order to retract the electronic motor on the rear axle to allow the piston to retract.
You can do this at home if you have a scan too. If you do not have a scan tool it is still possible to do it manually by disconnecting and removing the EPB servo and manually retracting, but it tricky and not recommended.
They use triple square fasteners on the bracket, and are typically a pain in the ass for this make.
Is there something else I'm missing?