Nissan Menlyn service nightmare

Sent my Nissan Navara 2014 model to Nissan Menlyn after I purchased it from a Mazda dealer is JHB south. It had a whining noise coming from the engine and Nissan Menlyn diagnosed it to be the timing chain. The quoted on the job and Mazda dealer paid for the repairs which we subsequently done by Nissan Menlyn. When I collected my vehicle the noise was still present and I alerted Nissan Menlyn about it. The service manager at the time was handing over to a new service manager at the time which I understood. A week later I contacted them to follow up on the issue and it was said that I had to bring in the vehicle asap so they could sort put the issue. I took the vehicle to them where they proceeded to determine the issue. I was then told that the issue may relate to either the diesel or vacuum pumps. These were then stripped out of the vehicle and sent for assessment. The assessment came back and it was reported that the Diesel pump was not the cause of the noise and so they suspect the vacuum pump (which has no bearing which can make a rotational noise) to be making the cause. They then proceeded to tell me that the Diesel pump has an over fueling issue which would cost around R5000 to repair. They then told me that they need to replace the vacuum pump which cost much more than the timing chain and I needed to pay in the difference plus the labor to put the car back together (plus minus R20 000). As I did not agree with that (due to the fact that the car was giving me close to 12km/l and the vacuum pump could not make the noise) I told them to rather put my car back together as they found it as they seem to be unable to identify and fix the issue. Now we are sitting almost 2 and and half months later (since I took it there) and they still haven't fixed or returned my vehicle. The biggest issue being that that now I will get my car back in exactly the same state as it was in before it went to Nissan as I am fed up with the poor service and lies. I also don't (according to them) any warranty on the initial timing chain job as they agreed to refund my money (R15 000). Is this how Nissan deals with misdiagnosed problems???