Cutting corners in repairs

I was told by the service adviser that my gearbox is damage inside & they ordered a new gearbox. Then I was send to the service manager for a curtesy car & he refused to assist me with one then we had a quarrel over it & I left. He(S/manager) send me a massage saying he has stopped repairs on my car & I must make arrangement to fetch it. I insisted on my car to be repaired. Few days later the service adviser called me to inform me that my car is ready for collection & I went all to find that they changed only the mechatronic sensor & I asked him what to the changing of the gearbox & he told me that he was instructed to change only the mechatronic sensor to cut the cost. I didn't want to mention this because he asked me not to because he might loose his job but now it leave me no choice but to mention it because my car gearbox is being giving problem ever since & I complained to Audi SA & they failed to assist me. I took it to Audi Arcadia they also failed to assist me. Furthermore the service manager at Arcadia even insulted me. I've been send from pillar to post, I don't know if it's because I'm black & they are all white & it's a reason they ill treated me so