No refund due to not caring

I rented a car from Avis for 10 Months. They will not refund my deposit. I did a full spreadsheet proving the refund and they keep still saying they cannot assist, their hands are tied. i have on email that my month runs 28th to 28th, I returned the car on the 28th. I get told the actual date was 23rd. They want to charge me R6773.22 for 5 days. That is what I paid monthly. I spent R67 732.20 and this is the service I receive. It is pathetic and I will not leave it here. I am reporting this to the Consumer commission, lay a civil complaint as well as every social platform available. I will not be unjustly treated by avis