Failer to diagnose my car

A 2 months ago I took my car(Nissan Navara 2016 model for checkup because it was showing oil light( oil low) and they open it. Their answers were 2( the computer box needed to be restarted and the oil was thin, I must make sure I bring my car for service in time for 45 000 so that they can change the oil filter and the oil. They further disconnected the battery and the light was off and I drove home. The following morning when I switched on the car the light came back again. I did as I was told by taking the car for service as early as possible, the car was serviced, they changed the oil filter and did some other service on the car, the light was off and I was happy, I took my car to the mall it was fine, but when I switched on at the mall the 'oil low' light came back and I drove home. The following day it was Saturday when Nissan polokwane called me to rate their service and I rated them 3 because I wasn't happy and they called me on Monday to bring back the car for recheck. When I took it back they said is Oil switch and is not covered on maintenance plan since is electronic device. Ohk fine I paid for the part and and they ordered it but still after the part was inserted it was still giving the oil problem. They then said they're going to check the cluster from the same model of the car and check if the problem is not the cluster. If they tried deferent clusters the problem is still there. Today(13/10/2017) 2 weeks after they started fixing the oil light they can't find the problem and my friends adviced me to take the car before they can worsen the problem but when I came here they told me that they can't give me the car because is dismantled and they'll finish putting everything back on Monday. I'm so disappointed from Nissan polokwane...