My magnite has been with the dealership for 3 months

So my magnite which is on 20000kms showed a sign on the dashboard saying "check antipollution system" and didn't have power 15 days ago. Nissan towed the car to TN Nissan Groblersdal the following day. And till to this day the dealer have no clue on what's wrong with the car. They said they changed the oxygen sensor which they thought might be the problem but it didn't work. And also said they changed the transmission control module but still today they can't tell me anything. It's been 3 months and the car is still at the dealership TM Nissan Groblersdal, waiting to be transported to witbank for further diagnosis.