Request for curtousy car

On the 29th I have taken my car for service at Mercedes Benz polokwane and was told that it will be ready by 17h00 then I went there at around 16h30 only to find that my car was having a problem which was discovered after a test drive that it was supposed to be programmed which is going to take few hours and was told that I will get my car the next day, later at around 15h00 was told that it's giving them a problem they are failing to fix my car and it's not advisable to drive it which is understandable . I have requested them to give me a curtousy car and was told that I have to pay R10000. 00 upfront for deposit which I don't have and feel that it's not fair because it's not my fault if they are failing to fix my car. And my challenge is I'm struggling to go to work as that is my only car I find it frustrating. Please intervened. Regards Harriet.