If you don’t service your car with Nissan. Your warranty apparently falls away. We are now forced

I bought my datsun go brand new from Nissan Sunninghill about 2.5 years back ( currently 55000km mileage). Recently I had a problem with my wheels and when I took the car to tyremart they told me the axel is bent. I took the car to Nissan star Vereeniging since it’s under warranty. I explained to them that my book was misplaced during relocation however I provided them with the slip of the last full service and a recent report of the 4-tyre replacements and wheel alignment. I just received an email now that Nissan only fixes cars if you service with Nissan only. No other approved and certified car place is supposed to touch your car. This was never mentioned to me and I didn’t know we don’t have freedom to choose where our cars get serviced. Most importantly I do not understand how it nullifies the warranty. ????my car has been at the store for over 3 weeks now. First you gave the wrong diagnosis that there’s nothing wrong with the axel without proper inspection and said warranty won’t cover it, after I raise a compliant to NSA only then was the matter taken further and now you found a problem with the axel like I initially stated when I brought in the car. And still warranty don’t cover it. I could have left with a broken car because your staff neglected to examine the car properly first time , endangering myself and my daughters life. I have been struggling to get to work because I was refused a courtesy car. Three weeks. Is this a new rule that we were not made aware of ?