Avis refuses to refund me... unacceptable!

In March this year I rented a car from Avis, had to return it before my rental period was completed. There was no issues and the remainder of my rental amount was refunded within 12 days. Now in August I rented a car and returned it after 7 days out of my 14 day rental. No one is able to do my refund of R2317.75 even after getting an invoice stating a refund is due. After 2 months of trying to get my refund, now I am told that Avis does not do refund of unused days! Nowhere does it state on my contract that unused days are lost! Totally unacceptable and comes down to taking my money and *****ing it! Person I am dealing with is Gontse Kgonothi who obviously doesn't gives a rat's ass about this.