AVIS Car Hire NOT HONEST TO DEAL WITH as they change thing on the fly without telling.

I was given a weekend free pass Group A for a 3 day free use of a vehicle and on the weekend of 26 - 28 went to Cape Town and collected a vehicle at Cape International. Upon arrival at vehicle collection and the front realised that my luggage was too big for a group A vehicle, I was advised that I can upgrade to a group B car and only pay an additional R50/day extra on top of the voucher. Yet a week later I get billed an invoice of R1100.