We purchased a new 2017 GLC300 4Matic in 12/2016.  Initially it was fulfilling our needs, then 6 months into it, the brakes started squeaking.  First only when backing up.  Recently it has been both backing up and when car is in full driving mode.  Worse, the squeak has now become a full grinding "metal on metal" sound, and seems to happen with regularity when in the cold.  

I have taken the car back to the dealership/shop about 5 to 6 times and they've kept the car for over 20 days in the shop over the course of their investigation, and have exchanged the brake pads and lining and the issue not only keeps coming back, it seems to be worsening.  

Anyone else know of or experiencing similar problems with MB vehicles?

Any help would be greatly appreciated.