CarFlexi-Flexible at *****ing your money

I rented a car through CarFlexi with voucher number CFE31131, the rental was from 21/08/2018 to 14/09/2018 and and insurance fee of R2880 was charged. I than had to return the car earlier on the 08/09/2018 and as per their General Terms of Use, I wanted to amend the contract so as to be charged for the days I only used the car. They flat out refused thus charging me for the 6days insurance fee of which I did not have the car for. Their prices are pro rated per day, yet they refused to pay back my money. I really hope someone can assist me with this day light *******. Until than I advise you to stay away from such businesses that only think of their pockets. STAY AWAY FROM CARFLEXI