No Refund when booking change

I made a booking last week for 4 days for a Large vehicle and paid R11 138 for the 4 days . Our situation change and I then had to change the booking the next day from 4 days to 3 days , only to be told that they don't do refunds. I had to choose extras to make up for the one day but I already chose all the extras when I first made the booking ( extra driver , road side assistance etc) but they still told me I need to add additional extras to cover for the 1 day. So I lost R2000 just like that.... Further to this I received and email that remaining funds for the 1 days not used will go towards extra charges that might have been incurred during the rentals . But again the agent who assisted me told me that, that cant happen and I had to make an additional R 3100 payment towards extra km that was driven. So I lost the 1 day=R2000 and still had to pay for the extra km's. So please people make sure life dont happen so that you have to make any changes to your booking with Avis.. God forbid. Pathetic service!!!