poor service and unexplanable overcharges. Empty promises of refunding my money

I hired a car at Dollar thrifty in Mthatha airport on the 22nd May 2020. After paying for everything including additional driver as well as delivery at a different location, I took the car. Later on after returning the car dollar thrifty made additional charges for two consecutive days with no explanation or sms notifying me what the charges were for. I struggled to get hold of them over the phone, and finally received an email address of Kathreen Kisten. I emailed to get explanation of what those charges were for. The explanation I received was that it was for delivery of car at a different loacation and additional driver. I told them that those were already charged how come they charge them twice? I later requested a statement showing a breakdown of these charges from initial charges. No response was provided to me. I was later promised by Kathreen that I would receive refund with seven days of the second additional charges, To this date, they have not refunded me. Whats even more depressing is that they do not pick up their phone and keep referring me, I don't know how much airtime I have wasted trying to contact dollar thrifty. The service is very poor and they are taking advantage of people.