Never prepay in full

I hired a car for 5 days prepaid, and in fairness I forgot some required documentation. They clearly stated that if I notified them 48 hours in advance that I would receive a refund. Let them know at time of pickup that I would not be able to give the required documentation and could therefore not hire. In my mind they require 48 hours to get the car rehired so in fairness I should pay for 2 days, however this company feels its entitled to the full 5 days. Not being able to hire a car ruined my holiday and on top of this they have capitalized on my misfortune so therefore cannot hire through them again.