Complimentary DOWNgrade???!!!!!

We traveled down to Durban over the weekend and booked a Group B vehicle with Europcar as we knew we would need the 5 doors and the boot space. When we arrived and collected the car we were given a VW Up! Its tiny, 2 doors and only the hand luggage could get in the ridiculous boot. Its a Group A vehicle but i was charged group B rates! The justification of it being a low mileage model means nothing to me when im using it for a long weekend!! Really not acceptable and im unimpressed.