Cheap quality for premium price

VW sold me a 2021 Polo TSI Comfortline with rear brake drums. This car doesn’t brake properly and it vibrates. I took it to a dealership and they said there’s nothing wrong with the brakes. The problem is that it only brakes with front discs n pressure is too much. So basically they downgraded the suspension from the 2014 Polo and put in the old Vivo suspension on the new shape TSI (which costs 200k more). I told them that I want to fit read discs to make the car safer and they threatened to cancel my warranty.