Taking tooo long to release my deposit and very poor service

The service is very poor! And unprofessional. Thrifty at OR Tambo is keeping my deposit, and they have been promising to send me a letter to take to my bank for the bank to release my deposit. I have been waiting for more than two weeks for my deposit. Firstly i was not informed that i will need a letter from them for the deposit when i hired the car. I had to go and enquire myself on my deposit, and by then they told me about my deposit. No one picks up calls for enquiries but they quickly pick up calls if u want to reserve a car. They take forever to respond to emails. I am really not sure whether it takes the whole company to draft and issue a letter to me.