Unhappy customer

I am driving a 2015 Toyota Land Cruiser LX V8 pick-up with 59000 kilo's on the odometer.

I have recently noticed a knocking sound when shifting between gears and when accelerating between gears. I took the vehicle to Monument Toyota Randfontein about 3 weeks ago to attend to the noise and was told that they think it is the gearbox. The gearbox was removed, checked and fitted again and told that the vehicle was fixed. I took the vehicle for a test drive with one of there mechanics, but it still had the same problem. I told them that it sounded to me like the front diff, which was removed and sent to a toyota approved specialist. I visited the specialist at his workshop (house) and was told that the diff was 100% and not the problem. The workshop manager said that they are first going to drive a new vehicle, as they are sure it is a common problem, before they do anything else. I informed them that i am going to call customer care, as the problem is still not resolved. I contacted customer care and explained my problem and was told that they will send out there specialist to attend to my problem. I was contacted by the workshop manager and informed that courtesy vehicle in my possession was sold and must be returned. I returned the courtesy vehicle and asked the service department, about the findings of the customer care specialist and was told that nobody from customer care came to see them

I have taken the vehicle to Rand Stadium Toyota & Monument Toyota Krugersdorp to listen to the noise, but was told that they would first need to drive a new vehicle (LX V8 pick- up), as they are sure that the noise was normal, but have not heard back from them at all. Please help me