RMI ACCREDITED DEALER NOT WORTHY OF NISSAN SERVICE, CAUSING WARRANTY ON VEHICLE TO BE VOIDED

So, i have a NP200 with 41500km on the clock, bought last year, the vehicle keeps overheating and the digital heat gauge in the vehicle is jumping from hot to normal in a matter of seconds, and this continues the whole trip.

If i drive on the hiway, the vehicle runs cool, if i stop at a robot etc, the heatgauge jumps up and down, indicating the vehicle overheats then its cool then it overheats etc.

Long story short, took the vehicle to Nissan in Nelspruit to be inspected as its still under warranty, so i thought. According to Nissan Nelspruit and Nissan SA, the warranty on this vehicle has been voided cause the air filter fitted by a registered RMI dealer is not a genuine NISSAN PART. The vehicle has had 2 services, 15000km and 30000km,all with the same RMI approved dealer, but because the air filter is not up to Nissan standard, the warranty is voided.

It seems like the thermostat on the vehice is faulty, words from Nissan Nelspruit ( Producta Nissan ) and this is caused due to the air filter not being a NISSAN APPROVED AIR FILTER. So, by my understanding, if we don't use water from a NISSAN marked bottle to replenish liquid in the vehicle, will it also void the warranty then??? Same with oil, same with coolant ???

A 15000km service at Nissan will cost close to R9k, labour alone is R6k, while a RMI registered dealer can do the same for under R5500, no Nissan this is ridiculous, so with this said, my vehicle is standing at Produkta Nissan, don't know till when.