Wrong vehicle and Overcharged

Reserfved an 8 passenger vehicle.  They don't have 8 passenger vehicles.  Was told $728 and charged $789.  Asked for a refund was told 2 to 4 days.  Need the refund now to rent the correct vehicle. Avis claims that there is no way to give money back the same day even though ANYONE who has used softwaer or charge machines knows you can.  Of coarse they have NO PROBLEM charging your account SAME DAY.  

This company needs to go under people.  
Stop using AVIS!!