Avis online booking deceptive misleading unhelpful

Very frustrated after trying to make a quick booking with Avis. I wanted to make a booking for a vehicle and entered my required details with dates required. Then wanted a super waiver package so entered the Super Waivers specials page as advertised. On the Super waivers specials page it wanted to recalculate my quote so clicked continue. I did not know that it changed my dates originally entered and and thought the quote was very \reasonable". I continued to pay for the booking and only after paying found out that it was a day short and the super waiver was not included. When I tried to amend the booking on the manage booking link"